This book is an outcome of research carried out for 5 years at Department of Botany, University of Pune, India in association with Department of Agricultural and Natural Resources, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran. The research was focused on interspecific competition and allelopathic effects of wild mustard and wild oat on growth and productivity of wheat. The book encompasses six chapters. Chapter-I is focused on weed-crop competition and factors influencing weed competition. Chapter-II is highlighting the previous work on this aspect on different food grains crop including wheat. Chapter-III includes the various types of methodology used, experimental design, crop density, weed density and nitrogen levels applied. Chapter-IV is focused on results of the different field, pot and Phytoextract bioassay experiments. Chapter-V is devoted to discuss the results and probable morpho-physiological characteristics of wheat competition ability of wheat,wild mustard and wild oat influeced by various dosses of nitrogen fertilizer. Chapter-VI, summary and conclussion are given in nutshell in last chapter. This book will be a guidline for agro-physiologist and weed biologist.