There is no other particle than the neutron which has attracted so much interest, both in fundamental physics and for applications. Because 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/16B, which has already been published, is completely dedicated to the data of neutron resonance parameters.