Difficult Conversations: How to Discuss What Matters Most
by Doug Stone, Bruce Patton, & Sheila Heen

The best book on what causes and what assists difficult conversations. Covers business situations as well as personal ones. Offers great tools to help you successfully have that difficult conversation with anyone.

Fierce Conversations: Achieving Success at Work & in Life, One Conversation at a Time
by Susan Scott

Susan Scott defines fierce as "robust, intense, strong, powerful, passionate, eager, unbridled" and that's exactly what she encourages and teaches in this great book on using conversations as profound tools for success.

Crucial Conversations: Tools for Talking When Stakes are High
by Patterson, Grenny, McMillan & Switzler

A great resource for learning the skills of effective conversation when emotions are high and disagreement is the issue.

Crucial Confrontations: Tools for resolving broken promises, violated expectations, and bad behavior
by Patterson, Grenny, McMillan & Switzler

Another awesome resource from the authors of the previous book. This one focuses more on holding people accountable and effectively dealing with others when they don't follow through on their agreements.

How the Way we Talk can Change the Way we Work: Seven Languages for Transformation
by Robert Kegan & Lisa Lasko Lahey

A great book that delves into language as a tool for personal and organizational effectiveness.

The Seven Principles for Making Marriage Work: A Practical Guide from the Country's Foremost Relationship Expert

A guidebook to making marriage work based on substantive research. Filled with examples and exercises to enrich and strengthen your marriage or other primary relationship. A world apart from your typical self-help relationship book.