diff --git a/Cargo.lock b/Cargo.lock
index 5a345c62699..e04d951f1b1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2619,7 +2619,7 @@ dependencies = [
 
 [[package]]
 name = "libp2p-core"
-version = "0.40.0"
+version = "0.40.1"
 dependencies = [
  "async-std",
  "either",
diff --git a/Cargo.toml b/Cargo.toml
index 189114f6ede..734b2d14efb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -68,7 +68,7 @@ libp2p = { version = "0.52.3", path = "libp2p" }
 libp2p-allow-block-list = { version = "0.2.0", path = "misc/allow-block-list" }
 libp2p-autonat = { version = "0.11.0", path = "protocols/autonat" }
 libp2p-connection-limits = { version = "0.2.1", path = "misc/connection-limits" }
-libp2p-core = { version = "0.40.0", path = "core" }
+libp2p-core = { version = "0.40.1", path = "core" }
 libp2p-dcutr = { version = "0.10.0", path = "protocols/dcutr" }
 libp2p-deflate = { version = "0.40.0", path = "transports/deflate" }
 libp2p-dns = { version = "0.40.0", path = "transports/dns" }
diff --git a/core/CHANGELOG.md b/core/CHANGELOG.md
index ecc1eff2d7a..2d5c47a1633 100644
--- a/core/CHANGELOG.md
+++ b/core/CHANGELOG.md
@@ -1,4 +1,11 @@
-## 0.40.0 
+## 0.40.1 - unreleased
+
+- Implement `Debug` for `StreamMuxerEvent`.
+  See [PR 4426].
+
+[PR 4426]: https://github.com/libp2p/rust-libp2p/pull/4426
+
+## 0.40.0
 
 - Allow `ListenerId` to be user-controlled, i.e. to be provided on `Transport::listen_on`.
   See [PR 3567].
diff --git a/core/Cargo.toml b/core/Cargo.toml
index e71c4d0f243..a3912f0f5e4 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -3,7 +3,7 @@ name = "libp2p-core"
 edition = "2021"
 rust-version = { workspace = true }
 description = "Core traits and structs of libp2p"
-version = "0.40.0"
+version = "0.40.1"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"
diff --git a/core/src/muxing.rs b/core/src/muxing.rs
index 13b826ba840..477e1608073 100644
--- a/core/src/muxing.rs
+++ b/core/src/muxing.rs
@@ -112,6 +112,7 @@ pub trait StreamMuxer {
 }
 
 /// An event produced by a [`StreamMuxer`].
+#[derive(Debug)]
 pub enum StreamMuxerEvent {
     /// The address of the remote has changed.
     AddressChange(Multiaddr),
diff --git a/swarm/CHANGELOG.md b/swarm/CHANGELOG.md
index bc035893bd4..77ddf3458d1 100644
--- a/swarm/CHANGELOG.md
+++ b/swarm/CHANGELOG.md
@@ -1,8 +1,12 @@
 ## 0.43.4 - unreleased
 
+- Implement `Debug` for event structs.
+  See [PR 4426].
+
 - Improve error message when `DialPeerCondition` prevents a dial.
   See [PR 4409].
 
+[PR 4426]: https://github.com/libp2p/rust-libp2p/pull/4426
 [PR 4409]: https://github.com/libp2p/rust-libp2p/pull/4409
 
 ## 0.43.3
diff --git a/swarm/src/behaviour.rs b/swarm/src/behaviour.rs
index 0ecdf7b31f0..d80f5f0c9a4 100644
--- a/swarm/src/behaviour.rs
+++ b/swarm/src/behaviour.rs
@@ -408,6 +408,7 @@ pub enum CloseConnection {
 
 /// Enumeration with the list of the possible events
 /// to pass to [`on_swarm_event`](NetworkBehaviour::on_swarm_event).
+#[derive(Debug)]
 pub enum FromSwarm<'a, Handler> {
     /// Informs the behaviour about a newly established connection to a peer.
     ConnectionEstablished(ConnectionEstablished<'a>),
@@ -450,7 +451,7 @@ pub enum FromSwarm<'a, Handler> {
 }
 
 /// [`FromSwarm`] variant that informs the behaviour about a newly established connection to a peer.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ConnectionEstablished<'a> {
     pub peer_id: PeerId,
     pub connection_id: ConnectionId,
@@ -464,6 +465,7 @@ pub struct ConnectionEstablished<'a> {
 /// This event is always paired with an earlier
 /// [`FromSwarm::ConnectionEstablished`] with the same peer ID, connection ID
 /// and endpoint.
+#[derive(Debug)]
 pub struct ConnectionClosed<'a, Handler> {
     pub peer_id: PeerId,
     pub connection_id: ConnectionId,
@@ -474,7 +476,7 @@ pub struct ConnectionClosed<'a, Handler> {
 
 /// [`FromSwarm`] variant that informs the behaviour that the [`ConnectedPoint`] of an existing
 /// connection has changed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct AddressChange<'a> {
     pub peer_id: PeerId,
     pub connection_id: ConnectionId,
@@ -484,7 +486,7 @@ pub struct AddressChange<'a> {
 
 /// [`FromSwarm`] variant that informs the behaviour that the dial to a known
 /// or unknown node failed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct DialFailure<'a> {
     pub peer_id: Option<PeerId>,
     pub error: &'a DialError,
@@ -496,7 +498,7 @@ pub struct DialFailure<'a> {
 ///
 /// This can include, for example, an error during the handshake of the encryption layer, or the
 /// connection unexpectedly closed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ListenFailure<'a> {
     pub local_addr: &'a Multiaddr,
     pub send_back_addr: &'a Multiaddr,
@@ -505,14 +507,14 @@ pub struct ListenFailure<'a> {
 }
 
 /// [`FromSwarm`] variant that informs the behaviour that a new listener was created.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct NewListener {
     pub listener_id: ListenerId,
 }
 
 /// [`FromSwarm`] variant that informs the behaviour
 /// that we have started listening on a new multiaddr.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct NewListenAddr<'a> {
     pub listener_id: ListenerId,
     pub addr: &'a Multiaddr,
@@ -521,40 +523,40 @@ pub struct NewListenAddr<'a> {
 /// [`FromSwarm`] variant that informs the behaviour that a multiaddr
 /// we were listening on has expired,
 /// which means that we are no longer listening on it.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ExpiredListenAddr<'a> {
     pub listener_id: ListenerId,
     pub addr: &'a Multiaddr,
 }
 
 /// [`FromSwarm`] variant that informs the behaviour that a listener experienced an error.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ListenerError<'a> {
     pub listener_id: ListenerId,
     pub err: &'a (dyn std::error::Error + 'static),
 }
 
 /// [`FromSwarm`] variant that informs the behaviour that a listener closed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ListenerClosed<'a> {
     pub listener_id: ListenerId,
     pub reason: Result<(), &'a std::io::Error>,
 }
 
 /// [`FromSwarm`] variant that informs the behaviour about a new candidate for an external address for us.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct NewExternalAddrCandidate<'a> {
     pub addr: &'a Multiaddr,
 }
 
 /// [`FromSwarm`] variant that informs the behaviour that an external address was confirmed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ExternalAddrConfirmed<'a> {
     pub addr: &'a Multiaddr,
 }
 
 /// [`FromSwarm`] variant that informs the behaviour that an external address was removed.
-#[derive(Clone, Copy)]
+#[derive(Debug, Clone, Copy)]
 pub struct ExternalAddrExpired<'a> {
     pub addr: &'a Multiaddr,
 }
diff --git a/swarm/src/handler.rs b/swarm/src/handler.rs
index dcc7ab1c09d..9374903f9b7 100644
--- a/swarm/src/handler.rs
+++ b/swarm/src/handler.rs
@@ -222,6 +222,42 @@ pub enum ConnectionEvent<'a, IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IO
     RemoteProtocolsChange(ProtocolsChange<'a>),
 }
 
+impl<'a, IP, OP, IOI, OOI> fmt::Debug for ConnectionEvent<'a, IP, OP, IOI, OOI>
+where
+    IP: InboundUpgradeSend + fmt::Debug,
+    IP::Output: fmt::Debug,
+    IP::Error: fmt::Debug,
+    OP: OutboundUpgradeSend + fmt::Debug,
+    OP::Output: fmt::Debug,
+    OP::Error: fmt::Debug,
+    IOI: fmt::Debug,
+    OOI: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ConnectionEvent::FullyNegotiatedInbound(v) => {
+                f.debug_tuple("FullyNegotiatedInbound").field(v).finish()
+            }
+            ConnectionEvent::FullyNegotiatedOutbound(v) => {
+                f.debug_tuple("FullyNegotiatedOutbound").field(v).finish()
+            }
+            ConnectionEvent::AddressChange(v) => f.debug_tuple("AddressChange").field(v).finish(),
+            ConnectionEvent::DialUpgradeError(v) => {
+                f.debug_tuple("DialUpgradeError").field(v).finish()
+            }
+            ConnectionEvent::ListenUpgradeError(v) => {
+                f.debug_tuple("ListenUpgradeError").field(v).finish()
+            }
+            ConnectionEvent::LocalProtocolsChange(v) => {
+                f.debug_tuple("LocalProtocolsChange").field(v).finish()
+            }
+            ConnectionEvent::RemoteProtocolsChange(v) => {
+                f.debug_tuple("RemoteProtocolsChange").field(v).finish()
+            }
+        }
+    }
+}
+
 impl<'a, IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IOI, OOI>
     ConnectionEvent<'a, IP, OP, IOI, OOI>
 {
@@ -262,6 +298,7 @@ impl<'a, IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IOI, OOI>
 /// of simultaneously open negotiated inbound substreams. In other words it is up to the
 /// [`ConnectionHandler`] implementation to stop a malicious remote node to open and keep alive
 /// an excessive amount of inbound substreams.
+#[derive(Debug)]
 pub struct FullyNegotiatedInbound<IP: InboundUpgradeSend, IOI> {
     pub protocol: IP::Output,
     pub info: IOI,
@@ -271,18 +308,20 @@ pub struct FullyNegotiatedInbound<IP: InboundUpgradeSend, IOI> {
 ///
 /// The `protocol` field is the information that was previously passed to
 /// [`ConnectionHandlerEvent::OutboundSubstreamRequest`].
+#[derive(Debug)]
 pub struct FullyNegotiatedOutbound<OP: OutboundUpgradeSend, OOI> {
     pub protocol: OP::Output,
     pub info: OOI,
 }
 
 /// [`ConnectionEvent`] variant that informs the handler about a change in the address of the remote.
+#[derive(Debug)]
 pub struct AddressChange<'a> {
     pub new_address: &'a Multiaddr,
 }
 
 /// [`ConnectionEvent`] variant that informs the handler about a change in the protocols supported on the connection.
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub enum ProtocolsChange<'a> {
     Added(ProtocolsAdded<'a>),
     Removed(ProtocolsRemoved<'a>),
@@ -352,7 +391,7 @@ impl<'a> ProtocolsChange<'a> {
 }
 
 /// An [`Iterator`] over all protocols that have been added.
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct ProtocolsAdded<'a> {
     protocols: Peekable<Difference<'a, StreamProtocol, RandomState>>,
 }
@@ -366,7 +405,7 @@ impl<'a> ProtocolsAdded<'a> {
 }
 
 /// An [`Iterator`] over all protocols that have been removed.
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct ProtocolsRemoved<'a> {
     protocols: Either<
         Peekable<Difference<'a, StreamProtocol, RandomState>>,
@@ -399,6 +438,7 @@ impl<'a> Iterator for ProtocolsRemoved<'a> {
 
 /// [`ConnectionEvent`] variant that informs the handler
 /// that upgrading an outbound substream to the given protocol has failed.
+#[derive(Debug)]
 pub struct DialUpgradeError<OOI, OP: OutboundUpgradeSend> {
     pub info: OOI,
     pub error: StreamUpgradeError<OP::Error>,
@@ -406,6 +446,7 @@ pub struct DialUpgradeError<OOI, OP: OutboundUpgradeSend> {
 
 /// [`ConnectionEvent`] variant that informs the handler
 /// that upgrading an inbound substream to the given protocol has failed.
+#[derive(Debug)]
 pub struct ListenUpgradeError<IOI, IP: InboundUpgradeSend> {
     pub info: IOI,
     pub error: IP::Error,
diff --git a/swarm/src/handler/map_in.rs b/swarm/src/handler/map_in.rs
index af828999b03..82cb12a183d 100644
--- a/swarm/src/handler/map_in.rs
+++ b/swarm/src/handler/map_in.rs
@@ -24,6 +24,7 @@ use crate::handler::{
 use std::{fmt::Debug, marker::PhantomData, task::Context, task::Poll};
 
 /// Wrapper around a protocol handler that turns the input event into something else.
+#[derive(Debug)]
 pub struct MapInEvent<TConnectionHandler, TNewIn, TMap> {
     inner: TConnectionHandler,
     map: TMap,
diff --git a/swarm/src/handler/map_out.rs b/swarm/src/handler/map_out.rs
index e92d1403ce6..8528b563ece 100644
--- a/swarm/src/handler/map_out.rs
+++ b/swarm/src/handler/map_out.rs
@@ -25,6 +25,7 @@ use std::fmt::Debug;
 use std::task::{Context, Poll};
 
 /// Wrapper around a protocol handler that turns the output event into something else.
+#[derive(Debug)]
 pub struct MapOutEvent<TConnectionHandler, TMap> {
     inner: TConnectionHandler,
     map: TMap,