Let the Nations Be Glad: The Supremacy of God in Missions by John Piper. One of the most thorough treatments of mission in our modern day, without being too scholarly.
What Is the Mission of the Church? Making Sense of Social Justice, Shalom, and the Great Commission by Kevin DeYoung and Greg Gilbert. Accessible answer to this very question.
When Helping Hurts: How to Alleviate Poverty Without Hurting the Poor… or Yourself by Steven Corbett and Brian Fikkert. This is a good overview of missions that corrects the fallacy that we simply need to go help people.
Multiply: Disciples Making Disciples by Francis Chan. This book is a useful resource for teaching, as each one of the twenty-four sections corresponds to an online video at www.multiplymovement.com. Chan and David Platt teach through each lesson in the book.
Gaining by Losing: Why the Future Belongs to Churches that Send by J.D.Greear. The true mission of the church is to train disciples and then send them out into the world.
Understanding Christian Mission: Participating in Suffering and Glory by Scott Sundquist. An historical and theological view into missiology.
Cross-Cultural Connections: Stepping Out and Fitting In Around the World by Duane Elmer. A practical guide for navigating cultural differences.
Living on Mission Journey Women Podcast with Gloria Furman (Journey Women Podcast episode 29)
NEXT Worldwide. This is an organization recommended as a partner for short-term youth mission trips that are grounded in biblical theology of missions and focused on evangelism and church planting. A great first step mission trip.
Operationworld.org. Operation World is a book, a website, a DVD set and a prayer ministry, all focused on missions and evangelism.
Articles on Rooted
Setting Expectations in Youth Missions by Nick Conner
How Acts Informs Our Summer Missions by Adam Peterson
Preparing Students for a Short Term Mission Trip by Philip Walkley
Three Reasons Why I Love Mission Trips by Mike Watt