Block from U+0400 to U+04FF. This block was introduced in Unicode version 1.1 (1993). It contains 256 codepoints.
The Wikipedia provides the following information on block Cyrillic:
Cyrillic is a Unicode block containing the characters used to write the most widely used languages with a Cyrillic orthography. The core of the block is based on the ISO 8859-5 standard, with additions for minority languages and historic orthographies.