You can now simplify your AWS CloudFormation template authoring by inserting references to existing CloudFormation templates using Include Transform. Transforms are declarative statements within CloudFormation templates that instruct CloudFormation how to process your template. Include Transform instructs CloudFormation on where in the main template to inject CloudFormation templates snippets stored in S3 buckets. For example, you can maintain your commonly used resource definitions as template snippets and use Include Transform to retrieve and include them into your main template to create or update stacks. Visit here to learn more.

Source: Amazon Web Services News AWS CloudFormation Supports Authoring Templates with Code References and Amazon VPC Peering