This book consists of 8 Chapters viz., (i) Basic Principles, (ii) Competition, (iii) Secondary Compounds, (iv) Non-contact coactions, (v) Antagonistic contact coactions, (vi) Synergic contact coactions, (vii) Conclusions, (viii) References and Appendix. It is hoped, that this book will provide inspiration and in-depth knowledge of the coactions and competition in higher plants.