diff --git a/src/identity/application/services/update_username/command.rs b/src/identity/application/services/update_username/command.rs
new file mode 100644
index 0000000..a0f6cdb
--- /dev/null
+++ b/src/identity/application/services/update_username/command.rs
@@ -0,0 +1,76 @@
+// SPDX-FileCopyrightText: 2024 Aravinth Manivannan <realaravinth@batsense.net>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use derive_getters::Getters;
+use serde::{Deserialize, Serialize};
+
+use super::*;
+
+#[derive(Clone, Debug, Serialize, Deserialize, Eq, PartialEq, Ord, PartialOrd, Getters)]
+pub struct UpdateUsernameCommand {
+    new_username: String,
+}
+
+impl UpdateUsernameCommand {
+    pub fn new(
+        new_username: String,
+        supplied_password: String,
+        actual_password_hash: &str,
+        config: &argon2_creds::Config,
+    ) -> IdentityCommandResult<Self> {
+        if !argon2_creds::Config::verify(actual_password_hash, &supplied_password).unwrap() {
+            return Err(IdentityCommandError::WrongPassword);
+        }
+        let new_username = config.username(&new_username)?;
+        Ok(Self { new_username })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cmd() {
+        let config = argon2_creds::Config::default();
+        let password = "adsfasdfasd";
+        let new_username = "realaravinth";
+        let hashed_password = config.password(password).unwrap();
+        assert_eq!(
+            UpdateUsernameCommand::new(
+                new_username.into(),
+                password.into(),
+                &hashed_password,
+                &config
+            )
+            .unwrap()
+            .new_username,
+            new_username
+        );
+
+        // username is not valid
+        assert!(matches!(
+            UpdateUsernameCommand::new(
+                "username".into(),
+                password.into(),
+                &hashed_password,
+                &config,
+            )
+            .err(),
+            Some(IdentityCommandError::BadUsername(_))
+        ));
+
+        // wrong password
+        assert_eq!(
+            UpdateUsernameCommand::new(
+                new_username.into(),
+                new_username.into(),
+                &hashed_password,
+                &config,
+            )
+            .err(),
+            Some(IdentityCommandError::WrongPassword)
+        );
+    }
+}
diff --git a/src/identity/application/services/update_username/events.rs b/src/identity/application/services/update_username/events.rs
new file mode 100644
index 0000000..a14a0f9
--- /dev/null
+++ b/src/identity/application/services/update_username/events.rs
@@ -0,0 +1,17 @@
+// SPDX-FileCopyrightText: 2024 Aravinth Manivannan <realaravinth@batsense.net>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use derive_getters::Getters;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, Serialize, Deserialize, Getters, Eq, PartialEq, Ord, PartialOrd)]
+pub struct UsernameUpdatedEvent {
+    username: String,
+}
+
+impl UsernameUpdatedEvent {
+    pub fn new(username: String) -> Self {
+        Self { username }
+    }
+}
diff --git a/src/identity/application/services/update_username/mod.rs b/src/identity/application/services/update_username/mod.rs
new file mode 100644
index 0000000..64f6317
--- /dev/null
+++ b/src/identity/application/services/update_username/mod.rs
@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: 2024 Aravinth Manivannan <realaravinth@batsense.net>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+pub mod command;
+pub mod events;
+pub mod service;
+use super::errors::*;
+
+#[async_trait::async_trait]
+pub trait UpdateUsernameUseCase {
+    async fn update_username(
+        &self,
+        cmd: command::UpdateUsernameCommand,
+    ) -> IdentityResult<events::UsernameUpdatedEvent>;
+}
diff --git a/src/identity/application/services/update_username/service.rs b/src/identity/application/services/update_username/service.rs
new file mode 100644
index 0000000..dda58bd
--- /dev/null
+++ b/src/identity/application/services/update_username/service.rs
@@ -0,0 +1,82 @@
+// SPDX-FileCopyrightText: 2024 Aravinth Manivannan <realaravinth@batsense.net>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+use super::*;
+use derive_builder::Builder;
+
+use super::*;
+use crate::identity::application::port::output::db::username_exists::*;
+
+#[derive(Builder)]
+pub struct UpdateUsernameService {
+    db_username_exists_adapter: UsernameExistsOutDBPortObj,
+}
+
+#[async_trait::async_trait]
+impl UpdateUsernameUseCase for UpdateUsernameService {
+    async fn update_username(
+        &self,
+        cmd: command::UpdateUsernameCommand,
+        //) -> errors::ProcessAuthorizationServiceResult<String>;
+    ) -> IdentityResult<events::UsernameUpdatedEvent> {
+        if self
+            .db_username_exists_adapter
+            .username_exists(cmd.new_username())
+            .await
+            .unwrap()
+        {
+            return Err(IdentityError::UsernameExists);
+        }
+
+        Ok(events::UsernameUpdatedEvent::new(cmd.new_username().into()))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::tests::bdd::*;
+
+    #[actix_rt::test]
+    async fn test_service() {
+        let new_username = "realaravinth";
+        let password = "password";
+        let config = argon2_creds::Config::default();
+        let hashed_password = config.password(password).unwrap();
+
+        let cmd = command::UpdateUsernameCommand::new(
+            new_username.into(),
+            password.into(),
+            &hashed_password,
+            &config,
+        )
+        .unwrap();
+
+        {
+            let s = UpdateUsernameServiceBuilder::default()
+                .db_username_exists_adapter(mock_username_exists_db_port(
+                    IS_CALLED_ONLY_ONCE,
+                    RETURNS_FALSE,
+                ))
+                .build()
+                .unwrap();
+            let res = s.update_username(cmd.clone()).await.unwrap();
+            assert_eq!(res.username(), cmd.new_username());
+        }
+
+        {
+            let s = UpdateUsernameServiceBuilder::default()
+                .db_username_exists_adapter(mock_username_exists_db_port(
+                    IS_CALLED_ONLY_ONCE,
+                    RETURNS_TRUE,
+                ))
+                .build()
+                .unwrap();
+            assert_eq!(
+                s.update_username(cmd.clone()).await.err(),
+                Some(IdentityError::UsernameExists)
+            );
+        }
+    }
+}