Mission is a core concept -- perhaps THE core concept -- of the New Testament. Clear, concise and comprehensive, no other text gives such wealth of study in these ancient documents on the theme of mission. Book studies, overviews, footnotes are all provided by true scholars in a readible format. So many launchpoints for dialogue are here. Much more important, this book will form conviction that moves us to engagement with our world. Mission is not just an idea. It demands courageous response in advancing God's loving work toward all peoples of the earth. Don't be put off by the academic format! Every paragraph is rich with insight cutting to the root of God's action and motivation toward all humanity. If you want to understand the truest essence of Christianity, read this book with Bible at your side...you will not see either God or yourself the same again.
This book has great insight and theology, but it was written by people way smarter than me! Seriously, I liked it a lot, but it is at a graduate reading level, and if you're just looking for casual reading, I'd suggest looking into some of the other suggestions above. If you want to go very in-depth, this is the book for you.