diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 0000000..ef69f54
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,69 @@
+//! Errors.
+
+use std::error::Error;
+use std::fmt;
+
+/// OAuth 2.0 error codes.
+///
+/// See [RFC 6749, section 5.2](http://tools.ietf.org/html/rfc6749#section-5.2).
+#[derive(Debug)]
+pub enum OAuth2ErrorCode {
+    /// The request is missing a required parameter, includes an unsupported parameter value (other
+    /// than grant type), repeats a parameter, includes multiple credentials, utilizes more than
+    /// one mechanism for authenticating the client, or is otherwise malformed.
+    InvalidRequest,
+
+    /// Client authentication failed (e.g., unknown client, no client authentication included, or
+    /// unsupported authentication method).
+    InvalidClient,
+
+    /// The provided authorization grant (e.g., authorization code, resource owner credentials) or
+    /// refresh token is invalid, expired, revoked, does not match the redirection URI used in the
+    /// authorization request, or was issued to another client.
+    InvalidGrant,
+
+    /// The authenticated client is not authorized to use this authorization grant type.
+    UnauthorizedClient,
+
+    /// The authorization grant type is not supported by the authorization server.
+    UnsupportedGrantType,
+
+    /// The requested scope is invalid, unknown, malformed, or exceeds the scope granted by the
+    /// resource owner.
+    InvalidScope,
+
+    /// An unrecognized error code, not defined in RFC 6749.
+    Unrecognized(String),
+}
+
+/// OAuth 2.0 error.
+///
+/// See [RFC 6749, section 5.2](http://tools.ietf.org/html/rfc6749#section-5.2).
+#[derive(Debug)]
+pub struct OAuth2Error {
+    /// Error code.
+    pub code: OAuth2ErrorCode,
+
+    /// Human-readable text providing additional information about the error.
+    pub description: Option<String>,
+
+    /// A URI identifying a human-readable web page with information about the error.
+    pub uri: Option<String>,
+}
+
+impl fmt::Display for OAuth2Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        try!(write!(f, "{:?}", self.code));
+        if let Some(ref description) = self.description {
+            try!(write!(f, ": {}", description));
+        }
+        if let Some(ref uri) = self.uri {
+            try!(write!(f, " ({})", uri));
+        }
+        Ok(())
+    }
+}
+
+impl Error for OAuth2Error {
+    fn description(&self) -> &str { "OAuth 2.0 API error" }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 5a66f01..b15d66f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17,4 +17,5 @@ extern crate url;
 
 pub mod token;
 pub mod provider;
+pub mod error;
 pub mod client;