Genomics is a new field of biology. Its fast development is caused mainly by quick progress in large-scale genome sequencing and in computer technology. In spite of a huge number of sequenced microbial genomes available in databases, their taxonomical diversity is biased and reflects the interests of researches and facility of microorganisms' isolation and culture in laboratory conditions. More than 80% of genome sequencing projects are focused on the members of Proteobacteria, Firmicutes and Actinobacteria. Environmental genome shotgun sequencing reveals that microbial diversity is much greater than we expected. Particular levels of genomic analysis, the problems and subjects of genomics are specified and described here.