diff --git a/src/conditional/if_modified_since.rs b/src/conditional/if_modified_since.rs
new file mode 100644
index 00000000..60a1b373
--- /dev/null
+++ b/src/conditional/if_modified_since.rs
@@ -0,0 +1,125 @@
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, IF_MODIFIED_SINCE};
+use crate::utils::{fmt_http_date, parse_http_date};
+
+use std::fmt::Debug;
+use std::option;
+use std::time::SystemTime;
+
+/// HTTP `IfModifiedSince` header
+///
+/// # Specifications
+///
+/// - [RFC 7232, section 3.3: If-Modified-Since](https://tools.ietf.org/html/rfc7232#section-3.3)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::conditional::IfModifiedSince;
+/// use std::time::{SystemTime, Duration};
+///
+/// let time = SystemTime::now() + Duration::from_secs(5 * 60);
+/// let expires = IfModifiedSince::new(time);
+///
+/// let mut res = Response::new(200);
+/// expires.apply(&mut res);
+///
+/// let expires = IfModifiedSince::from_headers(res)?.unwrap();
+///
+/// // HTTP dates only have second-precision.
+/// let elapsed = time.duration_since(expires.modified())?;
+/// assert_eq!(elapsed.as_secs(), 0);
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
+pub struct IfModifiedSince {
+    instant: SystemTime,
+}
+
+impl IfModifiedSince {
+    /// Create a new instance of `IfModifiedSince`.
+    pub fn new(instant: SystemTime) -> Self {
+        Self { instant }
+    }
+
+    /// Returns the last modification time listed.
+    pub fn modified(&self) -> SystemTime {
+        self.instant
+    }
+
+    /// Create an instance of `IfModifiedSince` from a `Headers` instance.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(IF_MODIFIED_SINCE) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If we successfully parsed the header then there's always at least one
+        // entry. We want the last entry.
+        let header = headers.iter().last().unwrap();
+
+        let instant = parse_http_date(header.as_str())?;
+        Ok(Some(Self { instant }))
+    }
+
+    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(IF_MODIFIED_SINCE, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        IF_MODIFIED_SINCE
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let output = fmt_http_date(self.instant);
+
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(output.into()) }
+    }
+}
+
+impl ToHeaderValues for IfModifiedSince {
+    type Iter = option::IntoIter<HeaderValue>;
+    fn to_header_values(&self) -> crate::Result<Self::Iter> {
+        // A HeaderValue will always convert into itself.
+        Ok(self.value().to_header_values().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::headers::Headers;
+    use std::time::Duration;
+
+    #[test]
+    fn smoke() -> crate::Result<()> {
+        let time = SystemTime::now() + Duration::from_secs(5 * 60);
+        let expires = IfModifiedSince::new(time);
+
+        let mut headers = Headers::new();
+        expires.apply(&mut headers);
+
+        let expires = IfModifiedSince::from_headers(headers)?.unwrap();
+
+        // HTTP dates only have second-precision
+        let elapsed = time.duration_since(expires.modified())?;
+        assert_eq!(elapsed.as_secs(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(IF_MODIFIED_SINCE, "<nori ate the tag. yum.>");
+        let err = IfModifiedSince::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+}
diff --git a/src/conditional/if_unmodified_since.rs b/src/conditional/if_unmodified_since.rs
new file mode 100644
index 00000000..8b9dbd7b
--- /dev/null
+++ b/src/conditional/if_unmodified_since.rs
@@ -0,0 +1,125 @@
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, IF_UNMODIFIED_SINCE};
+use crate::utils::{fmt_http_date, parse_http_date};
+
+use std::fmt::Debug;
+use std::option;
+use std::time::SystemTime;
+
+/// HTTP `IfUnmodifiedSince` header
+///
+/// # Specifications
+///
+/// - [RFC 7232, section 3.4: If-Unmodified-Since](https://tools.ietf.org/html/rfc7232#section-3.4)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::conditional::IfUnmodifiedSince;
+/// use std::time::{SystemTime, Duration};
+///
+/// let time = SystemTime::now() + Duration::from_secs(5 * 60);
+/// let expires = IfUnmodifiedSince::new(time);
+///
+/// let mut res = Response::new(200);
+/// expires.apply(&mut res);
+///
+/// let expires = IfUnmodifiedSince::from_headers(res)?.unwrap();
+///
+/// // HTTP dates only have second-precision.
+/// let elapsed = time.duration_since(expires.modified())?;
+/// assert_eq!(elapsed.as_secs(), 0);
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
+pub struct IfUnmodifiedSince {
+    instant: SystemTime,
+}
+
+impl IfUnmodifiedSince {
+    /// Create a new instance of `IfUnmodifiedSince`.
+    pub fn new(instant: SystemTime) -> Self {
+        Self { instant }
+    }
+
+    /// Returns the last modification time listed.
+    pub fn modified(&self) -> SystemTime {
+        self.instant
+    }
+
+    /// Create an instance of `IfUnmodifiedSince` from a `Headers` instance.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(IF_UNMODIFIED_SINCE) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If we successfully parsed the header then there's always at least one
+        // entry. We want the last entry.
+        let header = headers.iter().last().unwrap();
+
+        let instant = parse_http_date(header.as_str())?;
+        Ok(Some(Self { instant }))
+    }
+
+    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(IF_UNMODIFIED_SINCE, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        IF_UNMODIFIED_SINCE
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let output = fmt_http_date(self.instant);
+
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(output.into()) }
+    }
+}
+
+impl ToHeaderValues for IfUnmodifiedSince {
+    type Iter = option::IntoIter<HeaderValue>;
+    fn to_header_values(&self) -> crate::Result<Self::Iter> {
+        // A HeaderValue will always convert into itself.
+        Ok(self.value().to_header_values().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::headers::Headers;
+    use std::time::Duration;
+
+    #[test]
+    fn smoke() -> crate::Result<()> {
+        let time = SystemTime::now() + Duration::from_secs(5 * 60);
+        let expires = IfUnmodifiedSince::new(time);
+
+        let mut headers = Headers::new();
+        expires.apply(&mut headers);
+
+        let expires = IfUnmodifiedSince::from_headers(headers)?.unwrap();
+
+        // HTTP dates only have second-precision
+        let elapsed = time.duration_since(expires.modified())?;
+        assert_eq!(elapsed.as_secs(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(IF_UNMODIFIED_SINCE, "<nori ate the tag. yum.>");
+        let err = IfUnmodifiedSince::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+}
diff --git a/src/conditional/last_modified.rs b/src/conditional/last_modified.rs
new file mode 100644
index 00000000..110b7fa3
--- /dev/null
+++ b/src/conditional/last_modified.rs
@@ -0,0 +1,125 @@
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, LAST_MODIFIED};
+use crate::utils::{fmt_http_date, parse_http_date};
+
+use std::fmt::Debug;
+use std::option;
+use std::time::SystemTime;
+
+/// HTTP `LastModified` header
+///
+/// # Specifications
+///
+/// - [RFC 7232, section 2.2: Last-Modified](https://tools.ietf.org/html/rfc7232#section-2.2)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::conditional::LastModified;
+/// use std::time::{SystemTime, Duration};
+///
+/// let time = SystemTime::now() + Duration::from_secs(5 * 60);
+/// let last_modified = LastModified::new(time);
+///
+/// let mut res = Response::new(200);
+/// last_modified.apply(&mut res);
+///
+/// let last_modified = LastModified::from_headers(res)?.unwrap();
+///
+/// // HTTP dates only have second-precision.
+/// let elapsed = time.duration_since(last_modified.modified())?;
+/// assert_eq!(elapsed.as_secs(), 0);
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
+pub struct LastModified {
+    instant: SystemTime,
+}
+
+impl LastModified {
+    /// Create a new instance of `LastModified`.
+    pub fn new(instant: SystemTime) -> Self {
+        Self { instant }
+    }
+
+    /// Returns the last modification time listed.
+    pub fn modified(&self) -> SystemTime {
+        self.instant
+    }
+
+    /// Create an instance of `LastModified` from a `Headers` instance.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(LAST_MODIFIED) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If we successfully parsed the header then there's always at least one
+        // entry. We want the last entry.
+        let header = headers.iter().last().unwrap();
+
+        let instant = parse_http_date(header.as_str())?;
+        Ok(Some(Self { instant }))
+    }
+
+    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(LAST_MODIFIED, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        LAST_MODIFIED
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let output = fmt_http_date(self.instant);
+
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(output.into()) }
+    }
+}
+
+impl ToHeaderValues for LastModified {
+    type Iter = option::IntoIter<HeaderValue>;
+    fn to_header_values(&self) -> crate::Result<Self::Iter> {
+        // A HeaderValue will always convert into itself.
+        Ok(self.value().to_header_values().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::headers::Headers;
+    use std::time::Duration;
+
+    #[test]
+    fn smoke() -> crate::Result<()> {
+        let time = SystemTime::now() + Duration::from_secs(5 * 60);
+        let last_modified = LastModified::new(time);
+
+        let mut headers = Headers::new();
+        last_modified.apply(&mut headers);
+
+        let last_modified = LastModified::from_headers(headers)?.unwrap();
+
+        // HTTP dates only have second-precision
+        let elapsed = time.duration_since(last_modified.modified())?;
+        assert_eq!(elapsed.as_secs(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(LAST_MODIFIED, "<nori ate the tag. yum.>");
+        let err = LastModified::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+}
diff --git a/src/conditional/mod.rs b/src/conditional/mod.rs
index ca3db5ab..348e307e 100644
--- a/src/conditional/mod.rs
+++ b/src/conditional/mod.rs
@@ -9,5 +9,11 @@
 //! - [MDN: HTTP Conditional Requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests)
 
 mod etag;
+mod if_modified_since;
+mod if_unmodified_since;
+mod last_modified;
 
 pub use etag::ETag;
+pub use if_modified_since::IfModifiedSince;
+pub use if_unmodified_since::IfUnmodifiedSince;
+pub use last_modified::LastModified;