diff --git a/src/hash.rs b/src/hash.rs
index 70bb8095e8..e1fa568661 100644
--- a/src/hash.rs
+++ b/src/hash.rs
@@ -32,7 +32,7 @@ impl Error for InvalidHashAlgorithm {}
 
 /// A binary object ID.
 #[repr(C)]
-#[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq)]
+#[derive(Clone, Ord, PartialOrd, Eq, PartialEq)]
 pub struct ObjectID {
     pub hash: [u8; GIT_MAX_RAWSZ],
     pub algo: u32,
@@ -40,6 +40,27 @@ pub struct ObjectID {
 
 #[allow(dead_code)]
 impl ObjectID {
+    /// Return a new object ID with the given algorithm and hash.
+    ///
+    /// `hash` must be exactly the proper length for `algo` and this function panics if it is not.
+    /// The extra internal storage of `hash`, if any, is zero filled.
+    pub fn new(algo: HashAlgorithm, hash: &[u8]) -> Self {
+        let mut data = [0u8; GIT_MAX_RAWSZ];
+        // This verifies that the length of `hash` is correct.
+        data[0..algo.raw_len()].copy_from_slice(hash);
+        Self {
+            hash: data,
+            algo: algo as u32,
+        }
+    }
+
+    /// Return the algorithm for this object ID.
+    ///
+    /// If the algorithm set internally is not valid, this function panics.
+    pub fn algo(&self) -> Result<HashAlgorithm, InvalidHashAlgorithm> {
+        HashAlgorithm::from_u32(self.algo).ok_or(InvalidHashAlgorithm(self.algo))
+    }
+
     pub fn as_slice(&self) -> Result<&[u8], InvalidHashAlgorithm> {
         match HashAlgorithm::from_u32(self.algo) {
             Some(algo) => Ok(&self.hash[0..algo.raw_len()]),
@@ -55,6 +76,41 @@ impl ObjectID {
     }
 }
 
+impl Display for ObjectID {
+    /// Format this object ID as a hex object ID.
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let hash = self.as_slice().unwrap();
+        for x in hash {
+            write!(f, "{:02x}", x)?;
+        }
+        Ok(())
+    }
+}
+
+impl Debug for ObjectID {
+    /// Format this object ID as a hex object ID with a colon and name appended to it.
+    ///
+    /// ```
+    /// assert_eq!(
+    ///     format!("{:?}", HashAlgorithm::SHA256.null_oid()),
+    ///     "0000000000000000000000000000000000000000000000000000000000000000:sha256"
+    /// );
+    /// ```
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let hash = match self.as_slice() {
+            Ok(hash) => hash,
+            Err(_) => &self.hash,
+        };
+        for x in hash {
+            write!(f, "{:02x}", x)?;
+        }
+        match self.algo() {
+            Ok(algo) => write!(f, ":{}", algo.name()),
+            Err(e) => write!(f, ":invalid-hash-algo-{}", e.0),
+        }
+    }
+}
+
 /// A hash algorithm,
 #[repr(C)]
 #[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
@@ -192,3 +248,78 @@ pub mod c {
         pub fn hash_algo_ptr_by_number(n: u32) -> *const c_void;
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::HashAlgorithm;
+
+    fn all_algos() -> &'static [HashAlgorithm] {
+        &[HashAlgorithm::SHA1, HashAlgorithm::SHA256]
+    }
+
+    #[test]
+    fn format_id_round_trips() {
+        for algo in all_algos() {
+            assert_eq!(
+                *algo,
+                HashAlgorithm::from_format_id(algo.format_id()).unwrap()
+            );
+        }
+    }
+
+    #[test]
+    fn offset_round_trips() {
+        for algo in all_algos() {
+            assert_eq!(*algo, HashAlgorithm::from_u32(*algo as u32).unwrap());
+        }
+    }
+
+    #[test]
+    fn slices_have_correct_length() {
+        for algo in all_algos() {
+            for oid in [algo.null_oid(), algo.empty_blob(), algo.empty_tree()] {
+                assert_eq!(oid.as_slice().unwrap().len(), algo.raw_len());
+            }
+        }
+    }
+
+    #[test]
+    fn object_ids_format_correctly() {
+        let entries = &[
+            (
+                HashAlgorithm::SHA1.null_oid(),
+                "0000000000000000000000000000000000000000",
+                "0000000000000000000000000000000000000000:sha1",
+            ),
+            (
+                HashAlgorithm::SHA1.empty_blob(),
+                "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391",
+                "e69de29bb2d1d6434b8b29ae775ad8c2e48c5391:sha1",
+            ),
+            (
+                HashAlgorithm::SHA1.empty_tree(),
+                "4b825dc642cb6eb9a060e54bf8d69288fbee4904",
+                "4b825dc642cb6eb9a060e54bf8d69288fbee4904:sha1",
+            ),
+            (
+                HashAlgorithm::SHA256.null_oid(),
+                "0000000000000000000000000000000000000000000000000000000000000000",
+                "0000000000000000000000000000000000000000000000000000000000000000:sha256",
+            ),
+            (
+                HashAlgorithm::SHA256.empty_blob(),
+                "473a0f4c3be8a93681a267e3b1e9a7dcda1185436fe141f7749120a303721813",
+                "473a0f4c3be8a93681a267e3b1e9a7dcda1185436fe141f7749120a303721813:sha256",
+            ),
+            (
+                HashAlgorithm::SHA256.empty_tree(),
+                "6ef19b41225c5369f1c104d45d8d85efa9b057b53b14b4b9b939dd74decc5321",
+                "6ef19b41225c5369f1c104d45d8d85efa9b057b53b14b4b9b939dd74decc5321:sha256",
+            ),
+        ];
+        for (oid, display, debug) in entries {
+            assert_eq!(format!("{}", oid), *display);
+            assert_eq!(format!("{:?}", oid), *debug);
+        }
+    }
+}