ImprovLA is a popular workshop on long form improvisation founded by longtime improviser, actor, and comedian Keith Saltojanes, based in Los Angeles.
From the ImprovLA website:
Improv-LA is a place for improvisers, actors, and non-actors to come together to learn and strengthen their talent as a performer by focusing on the skills of long form improvisation. Whether you have no prior experience in improv or just want to get better, Improv-LA can help you.
Taught by veteran improviser and actor, Keith Saltojanes, has taken the concepts off all of his experience and training in both improvisation and acting and streamlined it into a workshop that can be the most beneficial for everyone involved.
Each sessions teaches skills to get better at long form improvisation, taught with very accessible terms and exercises, and culminates in a graduation show that puts to use all of the skills and tools learned during the session.Classes are kept small so each student will get more individual attention.
ImprovLA also hosts a podcast on learning long form improvisation.