Introduction-The Torah verses:
The Torah commands us that every seventh year one must sanctify the year as Shemitah. The Shemitah year entails a number of laws and regulations that relate to one’s land, ground produce, and loans. One is commanded to rest the land. One may not sow the field or prune the vineyards. One may not harvest the land regularly. The food is to be distributed equally to all, including animals. It is to be completely disowned for all to partake in. If these laws are guarded Hashem promises that the land will produce three years worth of produce in the 6th year. The lack of properly keeping the Shemitah laws is severely punished with exile from the land. One is also commanded in the Shemitah year to annul all loans that he is owed by other Jews.
The term Shemitah:
The term Shemitah is found in Devarim 15/2 with regards to the command of Shemitas Kesafim, abolishing loans. It means to let go or forgive. The term is not used in any of the earlier commands discussing the laws relating to the land during the Shemitah year. Rather the term “Shabbos” or “Sheviis” is used in the wording of these commands. Nevertheless the custom today is to use the term Shemitah to refer to the 7th year regarding all of its related matters and laws.
The reason behind the Mitzvah of Shemitah:
The purpose of the Mitzvah of Shemitah is for one to contemplate that Hashem created the world in 6 days. Alternatively it is in order for one to strengthen his Bitachon [trust] in Hashem. Alternatively it is for the land to rest from its constant production in order for it to be able to continue to produce vegetation in the future years.
In Kabala it is explained that during the Shemitah year the Sefirah of Malchus is elevated, similar to Shabbos. This is a cause for Simcha during this year. It is for this reason that the Tikkun of Rachel is not recited the entire year during Shemitah.
 Shemos 23/10-11; 34/21; Vayikra 25/1-7; 26/33-35; Re’e 15:2
 Vayikra 25/2 and 4
 Vayikra 25/4
 Vayikra 25/5
 Vayikra 25/6-7
 Shemos 23/11
 Vayikra 25/20-21
 Vayikra 26/33-34
 Re’e 15:2
 Chinuch Mishpatim Mitzvah 69
 Keli Yakar Behar
 Moreh Nevuchim, brought in Keli Yakar
 Kaf Hachaim 581/75