Exhibit 21

SUBSIDIARIES OF REGISTRANT

Clean Diesel Technologies, Inc.'s subsidiaries as of December 31, 2013 are listed below.

Name of Subsidiary |  | State/Jurisdiction of Incorporation |  | Common Equity Ownership
Clean Diesel Technologies Limited |  | United Kingdom |  | 100%
Catalytic Solutions, Inc. |  | California |  | 100%
CSI Aliso, Inc. |  | California |  | 100%
Catalytic Solutions Holdings, Inc. |  | Delaware |  | 100%
ECS Holdings, Inc. |  | Delaware |  | 100%
Engine Control Systems Ltd. |  | Nevada |  | 100%
Engine Control Systems Limited |  | New Brunswick |  | 100%
CDTI Sweden AB |  | Sweden |  | 100%