My suggestions for where to start…

Agile Retrospectives - Esther Derby & Diana Larsen
Tasty Cupcakes - Facilitation Techniques and Games
Retrospectives for Beginners
Reto-Mat
Specification by Example: How Successful Teams Deliver the Right Software - Gojko Adzic
User Story Mapping: Jeff Patton
Continuous Integration: Improving Software Quality and Reducing Risk - Paul Duvall
Little Book of Impediments - Tom Perry

Product Ownership

Agile Product Management - Roman Pichler
Agile Estimation and Planning - Mike Cohn
Story Mapping (Jeff Patton’s website)

Scrum Mastery

Scrum Mastery

Software Quality

Tools that create an automation script by recording use of a product are testing an implementation and tend to cost you more when you want to change your implementation.
Learning how to write tests that focus on the intent of what your product should do can (and should) be written BEFORE the implementation.
Some FREE testing and quality assessment tools that allow you to do that are here. They are all being continously improved.
Robot Framework
Fitnesse
Cucumber

Software quality: SonarQube
Metrics

Understanding ourselves, each other and working together…

The Culture Game - Daniel Mezick
The Design of Everyday Things - Donald Norman
Work Rules (at Google) - Laszlo Bock
Slack - Tom DeMarco
Creativity Inc. - Ed Catmull and Amy Wallace
Peopleware: Productive Projects and Teams - Tom DeMarco & Tim Lister
The Five Dysfunctions of a Team - Patrick Lencioni
Joy. Inc - Richard Sheridan
The Phoenix Project: A Novel about IT, DevOps, and Helping Your Business Win - Gene Kim
The DevOps Handbook - Gene Kim and Jez Humble
Thinking Fast and Slow - Daniel Kahneman
The Wisdom of Crowds - James Surowiecki
Flow - Mihaly Csikszentmihalyi
Software for your Head - Free book by Jim and Michele McCarthy
One From Many - Dee Hock (VISA and the rise of the chaordic organisation)
Orbiting the Giant Hairball - Gordon MacKenzie

How to write software that gets better and better as you make changes…

Extreme Programming Explained - Kent Beck
Clean Code: A Handbook of Agile Software Craftsmanship - Robert Martin
Growing Object-Oriented Software, Guided by Tests - Steve Freeman & Nat Pryce
Working Effectively with Legacy Code - Michael Feathers
The Pragmatic Programmer: From Journeyman to Master - Andrew Hunt & Dave Thomas
Agile Software Development Principles, Patterns, and Practices - Robert Martin
Refactoring: Improving the Design of Existing Code - Martin Fowler
Test Driven Development: By Example - Kent Beck

Finance…

Implementing Beyond Budgeting

Terms and Concepts…

Conway’s Law
Parkinson’s Law
Goodhart’s Law

Videos

Greatness
Participatory Organisations
Drive: What motivates us?
The Pattern of Living Systems
Cynefin Framework
Open Space - experience
Open Space - explanation
Reinvigorating Schools - Hamish Brewer

Useful websites…

OpenSpace Agility
Google’s Work Rules
Whole Team (Mob) Programming
Principles of Chaos Engineering (Netflix)
Enterprise Scrum
Behavioural Economics
Core Protocols
Large Scale Scrum (LeSS)
Marting Fowler’s (Manifesto Author) site
Bob Martin’s (Manifesto Author) site
Jerry Weinberg’s site
Brian Marick’s (Manifesto Author) site
History of Agile and related concepts
The original article that contributed to the naming of Scrum

Contracts…

18F - US Government
Agile Delivery Service RFQ - US Government
Agile Contracts
Flexible Contracts