diff --git a/bitreq/examples/custom_cert.rs b/bitreq/examples/custom_cert.rs
new file mode 100644
index 000000000..6d88aa8c9
--- /dev/null
+++ b/bitreq/examples/custom_cert.rs
@@ -0,0 +1,37 @@
+//! This example demonstrates the client builder with custom DER certificate.
+//! to run: cargo run --example custom_cert --features async-https-rustls
+
+#[cfg(not(feature = "async-https-rustls"))]
+fn main() {
+    println!("This example requires the 'async-https-rustls' feature.");
+}
+
+#[cfg(feature = "async-https-rustls")]
+fn main() -> Result<(), bitreq::Error> {
+    let runtime = tokio::runtime::Builder::new_current_thread()
+        .enable_io()
+        .build()
+        .expect("failed to build Tokio runtime");
+
+    runtime.block_on(request_with_client())
+}
+
+#[cfg(feature = "async-https-rustls")]
+async fn request_with_client() -> Result<(), bitreq::Error> {
+    let url = "http://example.com";
+    let cert_der = include_bytes!("../tests/test_cert.der");
+    let client = bitreq::Client::builder().with_root_certificate(cert_der.as_slice()).build();
+    // OR
+    // let cert_der: &[u8] = include_bytes!("../tests/test_cert.der");
+    // let client = bitreq::Client::builder().with_root_certificate(cert_der).build();
+    // OR
+    // let cert_vec: Vec<u8> = include_bytes!("../tests/test_cert.der").to_vec();
+    // let client = bitreq::Client::builder().with_root_certificate(cert_vec.as_slice()).build();
+
+    let response = client.send_async(bitreq::get(url)).await.unwrap();
+
+    println!("Status: {}", response.status_code);
+    println!("Body: {}", response.as_str()?);
+
+    Ok(())
+}
diff --git a/bitreq/src/client.rs b/bitreq/src/client.rs
index b5de6f2fb..28daf8536 100644
--- a/bitreq/src/client.rs
+++ b/bitreq/src/client.rs
@@ -9,6 +9,7 @@
 use std::collections::{hash_map, HashMap, VecDeque};
 use std::sync::{Arc, Mutex};
 
+use crate::connection::certificates::Certificates;
 use crate::connection::AsyncConnection;
 use crate::request::{OwnedConnectionParams as ConnectionKey, ParsedRequest};
 use crate::{Error, Request, Response};
@@ -39,10 +40,141 @@ struct ClientImpl<T> {
     connections: HashMap<ConnectionKey, Arc<T>>,
     lru_order: VecDeque<ConnectionKey>,
     capacity: usize,
+    client_config: Option<ClientConfig>,
+}
+
+pub struct ClientBuilder {
+    capacity: usize,
+    client_config: Option<ClientConfig>,
+}
+
+#[derive(Clone)]
+pub(crate) struct ClientConfig {
+    pub(crate) tls: Option<TlsConfig>,
+}
+
+#[derive(Clone)]
+pub(crate) struct TlsConfig {
+    pub(crate) certificates: Certificates,
+}
+
+impl TlsConfig {
+    fn new(cert_der: Vec<u8>) -> Self {
+        let certificates = Certificates::new(Some(cert_der)).expect("failed to append certificate");
+
+        Self { certificates }
+    }
+}
+
+/// Builder for configuring a `Client` with custom settings.
+///
+/// The builder allows you to set the connection pool capacity and add
+/// custom root certificates for TLS verification before constructing the client.
+///
+/// # Example
+///
+/// ```no_run
+/// # async fn example() -> Result<(), bitreq::Error> {
+/// use bitreq::{Client, RequestExt};
+///
+/// let cert_der = include_bytes!("../tests/test_cert.der");
+/// let client = Client::builder()
+///     .with_root_certificate(cert_der.as_slice())
+///     .with_capacity(20)
+///     .build();
+///
+/// let response = bitreq::get("https://example.com")
+///     .send_async_with_client(&client)
+///     .await?;
+/// # Ok(())
+/// # }
+/// ```
+impl ClientBuilder {
+    /// Creates a new `ClientBuilder` with default settings.
+    ///
+    /// Default configuration:
+    /// * `capacity` - 1 (single connection)
+    /// * `root_certificates` - None (uses system certificates)
+    pub fn new() -> Self { Self { capacity: 1, client_config: None } }
+
+    /// Adds a custom root certificate for TLS verification.
+    ///
+    /// The certificate must be provided in DER format. This method accepts any type
+    /// that can be converted into a `Vec<u8>`, such as `Vec<u8>`, `&[u8]`, or arrays.
+    /// This is useful when connecting to servers using self-signed certificates
+    /// or custom Certificate Authorities.
+    ///
+    /// # Arguments
+    ///
+    /// * `cert_der` - A DER-encoded X.509 certificate. Accepts any type that implements
+    ///   `Into<Vec<u8>>` (e.g., `&[u8]`, `Vec<u8>`, or `[u8; N]`).
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use bitreq::Client;
+    /// // Using a byte slice
+    /// let cert_der: &[u8] = include_bytes!("../tests/test_cert.der");
+    /// let client = Client::builder()
+    ///     .with_root_certificate(cert_der)
+    ///     .build();
+    ///
+    /// // Using a Vec<u8>
+    /// let cert_vec: Vec<u8> = cert_der.to_vec();
+    /// let client = Client::builder()
+    ///     .with_root_certificate(cert_vec)
+    ///     .build();
+    /// ```
+    pub fn with_root_certificate<T: Into<Vec<u8>>>(mut self, cert_der: T) -> Self {
+        let tls_config = TlsConfig::new(cert_der.into());
+        self.client_config = Some(ClientConfig { tls: Some(tls_config) });
+        self
+    }
+
+    /// Sets the maximum number of connections to keep in the pool.
+    ///
+    /// When the pool reaches this capacity, the least recently used connection
+    /// is evicted to make room for new connections.
+    ///
+    /// # Arguments
+    ///
+    /// * `capacity` - Maximum number of cached connections
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use bitreq::Client;
+    /// let client = Client::builder()
+    ///     .with_capacity(10)
+    ///     .build();
+    /// ```
+    pub fn with_capacity(mut self, capacity: usize) -> Self {
+        self.capacity = capacity;
+        self
+    }
+
+    /// Builds the `Client` with the configured settings.
+    ///
+    /// Consumes the builder and returns a configured `Client` instance
+    /// ready to send requests with connection pooling.
+    pub fn build(self) -> Client {
+        Client {
+            r#async: Arc::new(Mutex::new(ClientImpl {
+                connections: HashMap::new(),
+                lru_order: VecDeque::new(),
+                capacity: self.capacity,
+                client_config: self.client_config,
+            })),
+        }
+    }
+}
+
+impl Default for ClientBuilder {
+    fn default() -> Self { Self::new() }
 }
 
 impl Client {
-    /// Creates a new `Client` with the specified connection cache capacity.
+    /// Creates a new `Client` with the specified connection pool capacity.
     ///
     /// # Arguments
     ///
@@ -54,10 +186,14 @@ impl Client {
                 connections: HashMap::new(),
                 lru_order: VecDeque::new(),
                 capacity,
+                client_config: None,
             })),
         }
     }
 
+    /// Create a builder for a client
+    pub fn builder() -> ClientBuilder { ClientBuilder::new() }
+
     /// Sends a request asynchronously using a cached connection if available.
     pub async fn send_async(&self, request: Request) -> Result<Response, Error> {
         let parsed_request = ParsedRequest::new(request)?;
@@ -77,7 +213,13 @@ impl Client {
         let conn = if let Some(conn) = conn_opt {
             conn
         } else {
-            let connection = AsyncConnection::new(key, parsed_request.timeout_at).await?;
+            let client_config = {
+                let state = self.r#async.lock().unwrap();
+                state.client_config.clone()
+            };
+
+            let connection =
+                AsyncConnection::new(key, parsed_request.timeout_at, client_config).await?;
             let connection = Arc::new(connection);
 
             let mut state = self.r#async.lock().unwrap();
diff --git a/bitreq/src/connection.rs b/bitreq/src/connection.rs
index 37cbd12c6..ec76f8aff 100644
--- a/bitreq/src/connection.rs
+++ b/bitreq/src/connection.rs
@@ -22,6 +22,8 @@ use tokio::net::TcpStream as AsyncTcpStream;
 #[cfg(feature = "async")]
 use tokio::sync::Mutex as AsyncMutex;
 
+#[cfg(feature = "async")]
+use crate::client::ClientConfig;
 use crate::request::{ConnectionParams, OwnedConnectionParams, ParsedRequest};
 #[cfg(feature = "async")]
 use crate::Response;
@@ -29,6 +31,8 @@ use crate::{Error, Method, ResponseLazy};
 
 type UnsecuredStream = TcpStream;
 
+#[cfg(feature = "rustls")]
+pub(crate) mod certificates;
 #[cfg(feature = "rustls")]
 mod rustls_stream;
 #[cfg(feature = "rustls")]
@@ -266,15 +270,13 @@ impl AsyncConnection {
     pub(crate) async fn new(
         params: ConnectionParams<'_>,
         timeout_at: Option<Instant>,
+        client_config: Option<ClientConfig>,
     ) -> Result<AsyncConnection, Error> {
         let future = async move {
             let socket = Self::connect(params).await?;
 
             if params.https {
-                #[cfg(not(feature = "tokio-rustls"))]
-                return Err(Error::HttpsFeatureNotEnabled);
-                #[cfg(feature = "tokio-rustls")]
-                rustls_stream::wrap_async_stream(socket, params.host).await
+                Self::wrap_async_stream(socket, params.host, client_config).await
             } else {
                 Ok(AsyncHttpStream::Unsecured(socket))
             }
@@ -298,6 +300,30 @@ impl AsyncConnection {
         }))))
     }
 
+    /// Call the correct wrapper function depending on whether client_configs are present
+    #[cfg(all(feature = "rustls", feature = "tokio-rustls"))]
+    async fn wrap_async_stream(
+        socket: AsyncTcpStream,
+        host: &str,
+        client_config: Option<ClientConfig>,
+    ) -> Result<AsyncHttpStream, Error> {
+        if let Some(client_config) = client_config {
+            rustls_stream::wrap_async_stream_with_configs(socket, host, client_config).await
+        } else {
+            rustls_stream::wrap_async_stream(socket, host).await
+        }
+    }
+
+    /// Error treatment function, should not be called under normal circustances
+    #[cfg(not(all(feature = "rustls", feature = "tokio-rustls")))]
+    async fn wrap_async_stream(
+        _socket: AsyncTcpStream,
+        _host: &str,
+        _client_config: Option<ClientConfig>,
+    ) -> Result<AsyncHttpStream, Error> {
+        Err(Error::HttpsFeatureNotEnabled)
+    }
+
     async fn tcp_connect(host: &str, port: u16) -> Result<AsyncTcpStream, Error> {
         #[cfg(feature = "log")]
         log::trace!("Looking up host {host}");
@@ -447,7 +473,7 @@ impl AsyncConnection {
                 };
                 (_internal) => {
                     let new_connection =
-                        AsyncConnection::new(request.connection_params(), request.timeout_at)
+                        AsyncConnection::new(request.connection_params(), request.timeout_at, None)
                             .await?;
                     *self.0.lock().unwrap() = Arc::clone(&*new_connection.0.lock().unwrap());
                     core::mem::drop(read);
@@ -806,7 +832,8 @@ async fn async_handle_redirects(
             let new_connection;
             if needs_new_connection {
                 new_connection =
-                    AsyncConnection::new(request.connection_params(), request.timeout_at).await?;
+                    AsyncConnection::new(request.connection_params(), request.timeout_at, None)
+                        .await?;
                 connection = &new_connection;
             }
             connection.send(request).await
diff --git a/bitreq/src/connection/certificates.rs b/bitreq/src/connection/certificates.rs
new file mode 100644
index 000000000..4bfb26a73
--- /dev/null
+++ b/bitreq/src/connection/certificates.rs
@@ -0,0 +1,63 @@
+#[cfg(feature = "rustls")]
+use rustls::RootCertStore;
+#[cfg(feature = "rustls-webpki")]
+use webpki_roots::TLS_SERVER_ROOTS;
+
+use crate::Error;
+
+#[derive(Clone)]
+pub(crate) struct Certificates {
+    pub(crate) inner: RootCertStore,
+}
+
+impl Certificates {
+    pub(crate) fn new(cert_der: Option<Vec<u8>>) -> Result<Self, Error> {
+        let certificates = Self { inner: RootCertStore::empty() };
+
+        if let Some(cert_der) = cert_der {
+            certificates.append_certificate(cert_der)
+        } else {
+            Ok(certificates)
+        }
+    }
+
+    #[cfg(feature = "rustls")]
+    pub(crate) fn append_certificate(mut self, cert_der: Vec<u8>) -> Result<Self, Error> {
+        let mut certificates = self.inner;
+        certificates
+            .add(&rustls::Certificate(cert_der))
+            .map_err(Error::RustlsAppendCert)?;
+        self.inner = certificates;
+        Ok(self)
+    }
+
+    #[cfg(feature = "rustls")]
+    pub(crate) fn with_root_certificates(mut self) -> Self {
+        let mut root_certificates = self.inner;
+
+        // Try to load native certs
+        #[cfg(feature = "https-rustls-probe")]
+        if let Ok(os_roots) = rustls_native_certs::load_native_certs() {
+            for root_cert in os_roots {
+                // Ignore erroneous OS certificates, there's nothing
+                // to do differently in that situation anyways.
+                let _ = root_certificates.add(&rustls::Certificate(root_cert.0));
+            }
+        }
+
+        #[cfg(feature = "rustls-webpki")]
+        {
+            #[allow(deprecated)]
+            // Need to use add_server_trust_anchors to compile with rustls 0.21.1
+            root_certificates.add_server_trust_anchors(TLS_SERVER_ROOTS.iter().map(|ta| {
+                rustls::OwnedTrustAnchor::from_subject_spki_name_constraints(
+                    ta.subject,
+                    ta.spki,
+                    ta.name_constraints,
+                )
+            }));
+        }
+        self.inner = root_certificates;
+        self
+    }
+}
diff --git a/bitreq/src/connection/rustls_stream.rs b/bitreq/src/connection/rustls_stream.rs
index 01a3c417f..530ba20c5 100644
--- a/bitreq/src/connection/rustls_stream.rs
+++ b/bitreq/src/connection/rustls_stream.rs
@@ -24,6 +24,8 @@ use webpki_roots::TLS_SERVER_ROOTS;
 use super::{AsyncHttpStream, AsyncTcpStream};
 #[cfg(all(feature = "native-tls", not(feature = "rustls"), feature = "tokio-native-tls"))]
 use super::{AsyncHttpStream, AsyncTcpStream};
+#[cfg(feature = "async")]
+use crate::client::ClientConfig as CustomClientConfig;
 use crate::Error;
 
 #[cfg(feature = "rustls")]
@@ -63,6 +65,15 @@ fn build_client_config() -> Arc<ClientConfig> {
     Arc::new(config)
 }
 
+#[cfg(feature = "rustls")]
+fn build_rustls_client_config(certificates: RootCertStore) -> Arc<ClientConfig> {
+    let config = ClientConfig::builder()
+        .with_safe_defaults()
+        .with_root_certificates(certificates)
+        .with_no_client_auth();
+    Arc::new(config)
+}
+
 #[cfg(feature = "rustls")]
 pub(super) fn wrap_stream(tcp: TcpStream, host: &str) -> Result<SecuredStream, Error> {
     #[cfg(feature = "log")]
@@ -106,6 +117,33 @@ pub(super) async fn wrap_async_stream(
     Ok(AsyncHttpStream::Secured(Box::new(tls)))
 }
 
+#[cfg(all(feature = "rustls", feature = "tokio-rustls"))]
+pub(super) async fn wrap_async_stream_with_configs(
+    tcp: AsyncTcpStream,
+    host: &str,
+    custom_client_config: CustomClientConfig,
+) -> Result<AsyncHttpStream, Error> {
+    #[cfg(feature = "log")]
+    log::trace!("Setting up TLS parameters for {host}.");
+    let dns_name = match ServerName::try_from(host) {
+        Ok(result) => result,
+        Err(err) => return Err(Error::IoError(io::Error::new(io::ErrorKind::Other, err))),
+    };
+
+    let mut certificates = custom_client_config.tls.unwrap().certificates;
+    certificates = certificates.with_root_certificates();
+
+    let client_config = build_rustls_client_config(certificates.inner);
+    let connector = TlsConnector::from(CONFIG.get_or_init(|| client_config).clone());
+
+    #[cfg(feature = "log")]
+    log::trace!("Establishing TLS session to {host}.");
+
+    let tls = connector.connect(dns_name, tcp).await.map_err(Error::IoError)?;
+
+    Ok(AsyncHttpStream::Secured(Box::new(tls)))
+}
+
 #[cfg(all(feature = "native-tls", not(feature = "rustls")))]
 pub type SecuredStream = TlsStream<TcpStream>;
 
diff --git a/bitreq/src/error.rs b/bitreq/src/error.rs
index 9eb4346d1..7014d73a2 100644
--- a/bitreq/src/error.rs
+++ b/bitreq/src/error.rs
@@ -19,6 +19,9 @@ pub enum Error {
     #[cfg(feature = "rustls")]
     /// Ran into a rustls error while creating the connection.
     RustlsCreateConnection(rustls::Error),
+    #[cfg(feature = "rustls")]
+    /// Ran into a rustls error while appending a certificate.
+    RustlsAppendCert(rustls::Error),
     #[cfg(feature = "native-tls")]
     /// Ran into a native-tls error while creating the connection.
     NativeTlsCreateConnection(native_tls::Error),
@@ -101,6 +104,8 @@ impl fmt::Display for Error {
 
             #[cfg(feature = "rustls")]
             RustlsCreateConnection(err) => write!(f, "error creating rustls connection: {}", err),
+            #[cfg(feature = "rustls")]
+            RustlsAppendCert(err) => write!(f, "error appending certificate: {}", err),
             #[cfg(feature = "native-tls")]
             NativeTlsCreateConnection(err) => write!(f, "error creating native-tls connection: {err}"),
             MalformedChunkLength => write!(f, "non-usize chunk length with transfer-encoding: chunked"),
@@ -143,6 +148,8 @@ impl error::Error for Error {
             InvalidUtf8InBody(err) => Some(err),
             #[cfg(feature = "rustls")]
             RustlsCreateConnection(err) => Some(err),
+            #[cfg(feature = "rustls")]
+            RustlsAppendCert(err) => Some(err),
             _ => None,
         }
     }
diff --git a/bitreq/src/request.rs b/bitreq/src/request.rs
index 2f1755782..9271a5ce9 100644
--- a/bitreq/src/request.rs
+++ b/bitreq/src/request.rs
@@ -338,7 +338,7 @@ impl Request {
     #[cfg(feature = "async")]
     pub async fn send_async(self) -> Result<Response, Error> {
         let parsed_request = ParsedRequest::new(self)?;
-        AsyncConnection::new(parsed_request.connection_params(), parsed_request.timeout_at)
+        AsyncConnection::new(parsed_request.connection_params(), parsed_request.timeout_at, None)
             .await?
             .send(parsed_request)
             .await
diff --git a/bitreq/tests/main.rs b/bitreq/tests/main.rs
index 8d357f354..e59c81e34 100644
--- a/bitreq/tests/main.rs
+++ b/bitreq/tests/main.rs
@@ -16,6 +16,34 @@ async fn test_https() {
     assert_eq!(get_status_code(bitreq::get("https://example.com")).await, 200);
 }
 
+#[tokio::test]
+#[cfg(feature = "rustls")]
+async fn test_https_with_client() {
+    setup();
+    let client = bitreq::Client::new(1);
+    let response = client.send_async(bitreq::get("https://example.com")).await.unwrap();
+    assert_eq!(response.status_code, 200);
+}
+
+#[tokio::test]
+#[cfg(feature = "rustls")]
+async fn test_https_with_client_builder() {
+    setup();
+    let client = bitreq::Client::builder().build();
+    let response = client.send_async(bitreq::get("https://example.com")).await.unwrap();
+    assert_eq!(response.status_code, 200);
+}
+
+#[tokio::test]
+#[cfg(feature = "rustls")]
+async fn test_https_with_client_builder_and_cert() {
+    setup();
+    let cert_der = include_bytes!("test_cert.der");
+    let client = bitreq::Client::builder().with_root_certificate(cert_der.as_slice()).build();
+    let response = client.send_async(bitreq::get("https://example.com")).await.unwrap();
+    assert_eq!(response.status_code, 200);
+}
+
 #[tokio::test]
 #[cfg(feature = "json-using-serde")]
 async fn test_json_using_serde() {
diff --git a/bitreq/tests/test_cert.der b/bitreq/tests/test_cert.der
new file mode 100644
index 000000000..f8d4129e3
Binary files /dev/null and b/bitreq/tests/test_cert.der differ