The mishna which is part of the oral law, was written by the Tannaim in a short-form containing 6 volumes with 64 subvolumes.
The Mishna was composed by the Tanna Rabbi Yehuda Hanasi, often called Rebbi mostly quoting the disciples of Rabbi Akiva from whom the core of the Mishna stems from, as a means of making sure that the Torah SheBaal Peh (Oral Torah) would not be lost. It was written in a short form later expanded by the lengthier talmud-gemara.
The Mishna constitutes of Shisha Sedarim or Shas (six orders):
Each Seder deals with an overall topic, e.g.: Zra'im, meaning seeds, deals with topics pertaining to the land.