This is a review of the methods based on counting oligomers in nucleotide and amino acid sequences. Such methods are analogous to the formal linguistic analysis of human texts. This review includes methods based on the calculation of observed occurrences (frequencies) of oligomers and their distribution, as well as those based on deviations between the observed and the expected occurrences (contrast words, genome signatures) in biological sequences. Both types of methods have a wide range of sensitivity and can identify homologous as well as functionally and taxonomically related sequences.