Exhibit 21.1

List of Subsidiaries

Magnite CTV, Inc.

The Rubicon Project Australia PTY Limited

Rubicon Project Servicos De Internet Ltda

The Rubicon Project SARL

The Rubicon Project GmbH

Rubicon Project S.R.L.

Rubicon Project K.K.

The Rubicon Project Netherlands B.V.

The Rubicon Project Singapore Pte Ltd.

The Rubicon Project Limited

The Rubicon Project Canco, Inc.

RTK GmbH

RTK.io Inc.

Rubicon Project Apex, Inc.

5 Moon Media LLC

Rubicon Project Bell, Inc.

Rubicon Project Unlatch, Inc.

Rubicon Project Hopper, Inc.

Rubicon Project Daylight, Inc.

Project Daylight, LLC

The Rubicon Project Canada ULC

Telaria Ltd.

Telaria Holdings Pty Ltd

Telaria Pty Ltd

Telaria (Singapore) Pte Ltd

Telaria SDN. BHD.

Magnite CTV (NZ) Limited

Telaria Brazil Publicidade Ltda.

Telaria SAS

SlimCut Media Canada Inc.

ScanScout, Inc.

Tremor Video Canada, Inc.

Transpera, Inc.