Abstract
Lorentz and CPT symmetry represent cornerstones of our present understanding of nature, but may be violated in various theoretical approaches to underlying physics. Testing these symmetries therefore establishes a promising avenue to search for physics beyond the Standard Model. The canonical theoretical tool to identify possible experimental signatures of such violations is an effective-field-theory framework known as the Standard-Model Extension. This talk provides an overview of this topic with focus on efforts involving low-energy atomic and subatomic systems.