Lentil (Lens culinaris Medik) is one of the most rewarding rabi pulse crops in India and encloses inside its root nodules the microsymbiont Rhizobium leguminosarum. The crop is mostly cultivated in marginal or less fertile lands under rainfed condition, nodulated by soil rhizobia which vary greatly in infectivity and symbiotic effectiveness. Rhizobial inoculation gives variable response to lentil biomass and grain yield. Traditionally, isolation, testing, and selection of single strains with desired properties approach were applied for inoculant development. But still selection of strains is hampered even though the cracking of nodulation and N2-fixation genes in rhizobia. Various abiotic and biotic factors are known to influence the survival of root nodule bacteria in soil. Rhizobiophages are one of the potent biotic factors which play an important role in determining the survival, infectivity, and effectiveness of rhizobial strains in soil. This book currently provide the information regarding selection and the symbiotic performance of isolated phage susceptible/ resistant indigenous rhizobial strains and their interaction with host.