CHIANTI provides a database of atomic energy levels, wavelengths, radiative transition probabilities and electron excitation data for a large number of ions of as- trophysical interest. This database allows the calculation of theoretical line emissivities necessary for the analysis of optically thin emission line spectra, and includes also a suite of IDL (Interactive Data Language) programs to calculate optically thin synthetic spectra and to perform spectral analysis and plasma diagnostics. The rst version (1.0) of the CHIANTI database was released in 1996 (Dere et al. 1997) and has been exten- sively used for analysis of line spectra from astrophysical sources by the scientic community. The present paper describes the rst major update to the CHIANTI database which will subsequently be labeled version 2.0. The update consists of the addition of a large number of new ions, the revision of existing data for some ions and the inclusion of an IDL procedure to calculate the continuum. The CHIANTI atomic database and supporting IDL routines are freely available through the internet.