This document will provide string instrument players with principles, vocabulary, and procedures for communication and assessment that have, in my seven years of research with luthier Keith Hill (Brentwood, TN), made conversations about sound and playability comprehensible, precise, fearless, and useful. The three main chapters of this document (Chapters 2-4) contain the most essential takeaways from our research: Principles of Progress, A Language for Discussing Sound and Playability, and Quantitative Assessment. They lay the groundwork for productive collaboration, then explore the terminology needed to have meaningful conversations, and finally build a framework for analyzing and comparing those observations. It also includes a chapter of background (Chapter 1) that describes Keith’s formative influences and the creation of our research partnership. The principles, vocabulary, and procedures for communication and assessment are useful in many scenarios, including maintaining and improving the characteristics of an instrument, choosing and purchasing an instrument with confidence, understanding and playing to an instrument’s strengths and weaknesses, and discussing sound while teaching and rehearsing.