The functional analysis of plant-microbe interactions has re-emerged in the past 10 years due to spectacular advances in integrative study models. This book summarizes basic and technical information related to the plant growth promoting rhizobacteria (PGPR) belonging to the genus Azospirillum, considered to be one of the most representative PGPR last 40 years. We include exhaustive information about the general microbiology of genus Azospirillum, their identification strategies; the evaluation of plant growth promoting mechanisms, inoculants technology and agronomic use of these bacteria and some special references to the genetic technology and use.