Recorded 14 February 2023. Leonardo de Moura of Microsoft Research presents "The Lean proof assistant: introduction and challenges" at IPAM's Machine Assisted Proofs Workshop. Abstract: Lean is the proof assistant of choice for the mathematics community. It is also an efficient programming language, and users can extend Lean functionality using Lean itself. The Lean mathematical library (Mathlib) has more than one million lines of code and contributions from more than 200 people. This talk briefly introduces the Lean proof assistant and discusses the many challenges ahead. Learn more online at: http://www.ipam.ucla.edu/programs/workshops/machine-assisted-proofs/