A polyalphabetic (or mixed) block code is a set of codewords of finite length, where every symbol of a codeword belongs to its own alphabet. In contrast to previous publications we consider a general case, where we do not assume any algebraic structure of the alphabets and the codes. Upper and lower bounds on the cardinality of a polyalphabetic code with given Hamming distance are obtained. Some constructions of polyalphabetic codes are suggested based on known codes. Encoding and decoding of the polyalphabetic codes, obtained in this way, can be done using encoding and decoding algorithms for the mother code. Using this constructions, codes are obtained, that reach the upper Singleton type bound.