diff --git a/examples/debug.rs b/examples/debug.rs
new file mode 100644
index 0000000..3d3018f
--- /dev/null
+++ b/examples/debug.rs
@@ -0,0 +1,17 @@
+use slotmap::SlotMap;
+
+slotmap::new_key_type! { struct CustomKey; }
+
+fn main() {
+    let mut x: SlotMap<CustomKey, &'_ str> = SlotMap::with_key();
+    let k0 = x.insert("a");
+    x.insert("b");
+    x.insert("c");
+    dbg!(&x);
+
+    x.remove(k0);
+
+    x.insert("later");
+
+    dbg!(x);
+}
diff --git a/src/basic.rs b/src/basic.rs
index 0666ed6..8f133e7 100644
--- a/src/basic.rs
+++ b/src/basic.rs
@@ -12,6 +12,7 @@ use core::marker::PhantomData;
 #[allow(unused_imports)] // MaybeUninit is only used on nightly at the moment.
 use core::mem::{ManuallyDrop, MaybeUninit};
 use core::ops::{Index, IndexMut};
+use std::fmt::Debug;
 
 use crate::{DefaultKey, Key, KeyData};
 
@@ -109,7 +110,7 @@ impl<T: fmt::Debug> fmt::Debug for Slot<T> {
 /// Slot map, storage with stable unique keys.
 ///
 /// See [crate documentation](crate) for more details.
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct SlotMap<K: Key, V> {
     slots: Vec<Slot<V>>,
     free_head: u32,
@@ -117,6 +118,16 @@ pub struct SlotMap<K: Key, V> {
     _k: PhantomData<fn(K) -> K>,
 }
 
+impl<K: Debug + Key, V: Debug> Debug for SlotMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_map();
+        for (k, v) in self.iter() {
+            f.entry(&k, v);
+        }
+        f.finish()
+    }
+}
+
 impl<V> SlotMap<DefaultKey, V> {
     /// Constructs a new, empty [`SlotMap`].
     ///
diff --git a/src/dense.rs b/src/dense.rs
index 926e3bc..cce454d 100644
--- a/src/dense.rs
+++ b/src/dense.rs
@@ -9,6 +9,7 @@
 #[cfg(all(nightly, any(doc, feature = "unstable")))]
 use alloc::collections::TryReserveError;
 use alloc::vec::Vec;
+use core::fmt::{self, Debug};
 use core::iter::FusedIterator;
 #[allow(unused_imports)] // MaybeUninit is only used on nightly at the moment.
 use core::mem::MaybeUninit;
@@ -30,7 +31,7 @@ struct Slot {
 /// Dense slot map, storage with stable unique keys.
 ///
 /// See [crate documentation](crate) for more details.
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct DenseSlotMap<K: Key, V> {
     keys: Vec<K>,
     values: Vec<V>,
@@ -38,6 +39,16 @@ pub struct DenseSlotMap<K: Key, V> {
     free_head: u32,
 }
 
+impl<K: Debug + Key, V: Debug> Debug for DenseSlotMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_map();
+        for (k, v) in self.iter() {
+            f.entry(&k, v);
+        }
+        f.finish()
+    }
+}
+
 impl<V> DenseSlotMap<DefaultKey, V> {
     /// Construct a new, empty [`DenseSlotMap`].
     ///
diff --git a/src/hop.rs b/src/hop.rs
index 57e7857..6b3baa9 100644
--- a/src/hop.rs
+++ b/src/hop.rs
@@ -17,7 +17,7 @@
 #[cfg(all(nightly, any(doc, feature = "unstable")))]
 use alloc::collections::TryReserveError;
 use alloc::vec::Vec;
-use core::fmt;
+use core::fmt::{self, Debug};
 use core::iter::FusedIterator;
 use core::marker::PhantomData;
 use core::mem::ManuallyDrop;
@@ -129,13 +129,23 @@ impl<T: fmt::Debug> fmt::Debug for Slot<T> {
 /// Hop slot map, storage with stable unique keys.
 ///
 /// See [crate documentation](crate) for more details.
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct HopSlotMap<K: Key, V> {
     slots: Vec<Slot<V>>,
     num_elems: u32,
     _k: PhantomData<fn(K) -> K>,
 }
 
+impl<K: Debug + Key, V: Debug> Debug for HopSlotMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_map();
+        for (k, v) in self.iter() {
+            f.entry(&k, v);
+        }
+        f.finish()
+    }
+}
+
 impl<V> HopSlotMap<DefaultKey, V> {
     /// Constructs a new, empty [`HopSlotMap`].
     ///
diff --git a/src/secondary.rs b/src/secondary.rs
index f7dc63d..4d9537c 100644
--- a/src/secondary.rs
+++ b/src/secondary.rs
@@ -4,6 +4,7 @@ use super::{is_older_version, Key, KeyData};
 #[cfg(all(nightly, any(doc, feature = "unstable")))]
 use alloc::collections::TryReserveError;
 use alloc::vec::Vec;
+use core::fmt::{self, Debug};
 use core::hint::unreachable_unchecked;
 use core::iter::{Enumerate, Extend, FromIterator, FusedIterator};
 use core::marker::PhantomData;
@@ -117,13 +118,23 @@ impl<T> Slot<T> {
 /// health[bob] -= ammo[alice] * 3;
 /// ammo[alice] = 0;
 /// ```
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct SecondaryMap<K: Key, V> {
     slots: Vec<Slot<V>>,
     num_elems: usize,
     _k: PhantomData<fn(K) -> K>,
 }
 
+impl<K: Debug + Key, V: Debug> Debug for SecondaryMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_map();
+        for (k, v) in self.iter() {
+            f.entry(&k, v);
+        }
+        f.finish()
+    }
+}
+
 impl<K: Key, V> SecondaryMap<K, V> {
     /// Constructs a new, empty [`SecondaryMap`].
     ///
@@ -1284,7 +1295,7 @@ impl<'a, K: Key, V> VacantEntry<'a, K, V> {
         // Despite the slot being considered Vacant for this entry, it might be occupied
         // with an outdated element.
         match replace(slot, Slot::new_occupied(self.kd.version.get(), value)) {
-            Occupied { .. } => {},
+            Occupied { .. } => {}
             Vacant => self.map.num_elems += 1,
         }
         unsafe { slot.get_unchecked_mut() }
diff --git a/src/sparse_secondary.rs b/src/sparse_secondary.rs
index 1e93a22..d2fac47 100644
--- a/src/sparse_secondary.rs
+++ b/src/sparse_secondary.rs
@@ -6,6 +6,7 @@ use alloc::collections::TryReserveError;
 #[allow(unused_imports)] // MaybeUninit is only used on nightly at the moment.
 use core::mem::MaybeUninit;
 use std::collections::hash_map::{self, HashMap};
+use std::fmt::{self, Debug};
 use std::hash;
 use std::iter::{Extend, FromIterator, FusedIterator};
 use std::marker::PhantomData;
@@ -65,12 +66,22 @@ struct Slot<T> {
 /// ammo[alice] = 0;
 /// ```
 
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub struct SparseSecondaryMap<K: Key, V, S: hash::BuildHasher = hash_map::RandomState> {
     slots: HashMap<u32, Slot<V>, S>,
     _k: PhantomData<fn(K) -> K>,
 }
 
+impl<K: Debug + Key, V: Debug, S: hash::BuildHasher> Debug for SparseSecondaryMap<K, V, S> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut f = f.debug_map();
+        for (k, v) in self.iter() {
+            f.entry(&k, v);
+        }
+        f.finish()
+    }
+}
+
 impl<K: Key, V> SparseSecondaryMap<K, V, hash_map::RandomState> {
     /// Constructs a new, empty [`SparseSecondaryMap`].
     ///