A method of controlling a user interface (5.M+1) of a user device (6.M+1) operated by a new participant (4.M+1) of an established communication event, the established communication event being conducted between a plurality of existing participants (4.1, 4.2, 4.M) by transmitting and receiving video streams via a communication network between user devices (6.2, 6.M) operated by those existing participants, the method comprising steps of: receiving a notification of the new participant joining the established communication event; determining, based on the received notification, whether the new participant satisfies a late-to-join condition based on at least one of an elapsed time of the communication event at a join time of the new participant, or a number of existing participants of the communication event at the join time of the new participant; and if the late-to-join condition is determined to be satisfied: controlling the user interface to operate in a late-to-join mode for an initial duration, wherein controlling the user interface to operate in a late-to-join mode comprises selecting for the new participant one of a video stream of a non-speaking participant or an avatar image of the non-speaking participant, and in response to expiry of the initial duration, controlling the user interface to operate in an active speaker mode instead; wherein controlling the user interface to operate in the active speaker mode comprises selecting for the new participant, based on audio data generated at the user device of an actively speaking one of the participants: one of a video stream of the actively speaking participant or an avatar image representing the actively speaking participant, thereby causing the user interface to display the selected avatar image or a video image derived from the selected stream. receiving a notification of the new participant joining the established communication event; determining, based on the received notification, whether the new participant satisfies a late-to-join condition based on at least one of an elapsed time of the communication event at a join time of the new participant, or a number of existing participants of the communication event at the join time of the new participant; and if the late-to-join condition is determined to be satisfied: controlling the user interface to operate in a late-to-join mode for an initial duration, wherein controlling the user interface to operate in a late-to-join mode comprises selecting for the new participant one of a video stream of a non-speaking participant or an avatar image of the non-speaking participant, and in response to expiry of the initial duration, controlling the user interface to operate in an active speaker mode instead; wherein controlling the user interface to operate in the active speaker mode comprises selecting for the new participant, based on audio data generated at the user device of an actively speaking one of the participants: one of a video stream of the actively speaking participant or an avatar image representing the actively speaking participant, thereby causing the user interface to display the selected avatar image or a video image derived from the selected stream.