There is no other particle than the neutron which has attracted so much interest, both in fundamental physics and for applications.-Because of no larger compilation of neutron data has appeared since more than 10 years, it seemed necessary, in particular for applications, to publish an up-to-date collection of such data.-The present compilation provides data for neutrons with energies lower than 20 MeV, with the emphasis on energies below the keV range.-There is such an abundance of experimental data that it had to be distributed over three volumes.-The fundamental properties of the neutron, the cross sections for various neutron reactions and some overall parameters of resonances are reproduced in the present subvolumes I/16A, Part 1 and Part 2, while Volume I/16 B, which has already been published , it completely dedicated to the data of neutron resonance parameters.