This Book describes the studies of field isolated Brucella melitensis, B.abortus in comparison with reference and vaccine strains. General bacteriological and serological examinations were used to isolate the organism from small ruminants (B. melitensis) and bovine species (B. abortus). omp31,omp2a and IS711 genes have been used as a target gene for PCR amplification to identify the field isolates and to differentiate between them. Cloning and sequencing of omp31 gene in this monograph showed 99% similarity to most Brucella omp31 genes. Further homology search for other omps of Brucella species revealed comparatively higher similarity (60.7%) with its counterpart omp31b gene sequences.The deduced amino acid alignment report of B. melitensis Omp31 also indicated about 97% identity with reported Brucella Omp31 proteins and less significant similarity with sequenced Omps from other bacteria.The western blot analysis performed on native OMP further confirmed that the Omp31 protein is one of the major immunodominant proteins in B. melitensis. Being the major OMP in B.melitensis & B.ovis strains, Omp31 might have a particular usefulness for vaccination against sheep and goat brucellosis.