About Agile Coaching
Lyssa Adkin’s book Coaching Agile Teams is a classic and still very relevant (now also available as audiobook).
You might think that Dale Carnegie’s classic ‘How to Win Friends & Influence People‘ might not have that much to do with coaching, but you might want to think again. Considerations such as ‘Does it have to said? Does it have to be said now? Does it have to be said by me?’ are all over this book and you have consider giving it a change if you have not already.
If you need a reminder on the Agile Coaching Competency Framework, have a look at the video.

Teaching
As much as you might not like using slides, it is sometimes inevitable. If you find that to be true, have a look at Presentation Zen.
Professional Coaching
Co-Active Coaching: New Skills for Coaching People Toward Success in Work and, Life is a really nice introduction work into the work of Professional Coaching.
The International Coaching Federation is one of the biggest coaching organizations in the world. Their certifications are probably the most widely recognized.
Organisation and Relationship Systems Coaching (O.R.S.C) is a style of coaching that focuses on groups of people and systems instead of individuals. It has been increasingly popular in the Agile Coaching world in recent years.
If you are looking for a safe place to practice your professional coaching skills the Agile Coaching Circles are free monthly Zoom calls to do just that. There are different calls for different timezones:
North America: https://www.meetup.com/icagile-coaching-circles/
Europe: https://www.meetup.com/european-agile-coaching-circle/
Africa: https://www.meetup.com/africa-agile-coaching-circle/
APAC-West: https://www.meetup.com/icagile-coaching-circles-apac-west/
APAC-East: https://www.meetup.com/icagile-coaching-circle-apac-east/
Mentoring
Facilitation
When it comes to facilitating Retrospectives, Agile Retrospectives is a still a classic.
As an alternative, I think that The Retrospective Handbook available at Leanpub is just as valuable, albeit not so famous.
Jimmy Janlen’s book ‘Toolbox for the Agile Coach – Visualization Examples ‘is a special one, focussing on visual facilitation only.
The best training on facilitation for anyone in the Agile space are Agile Team Facilitation training (although I cannot recommend a specific provider).
If you are looking for a training to specifically facilitate remote evens, Judy Rees has very practical trainings available.
Enterprise Level Agile Coaching
If you are interested in Enterprise-level Agile coaching, have a look at the corresponding track at ICAgile.
In Europe, Simon Powers at Adventures with Agile is the thought leader on this subject.