We will review the subject of line defects in d-dimensional Conformal Field Theories (CFTs). We discuss an exact formula governing the renormalization group flow on line defects and consider some examples involving line defects in 2,3, and 4 space-time dimensions. ---------------- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.