Part of the crop (rabbinically, 1/60) must be given to the priests, as it says "The first of your grain, wine and oil... you shall give him".¹ A tithe (a tenth) of the remainder is given to the Levites, as it says "And to the children of Levi I have given all tithes in Israel... for the tithe of the children of Israel that they lift up to Ha-Shem as a heave-offering I have given to the Levites".² (The Levite in turn gives a tithe of his tithe to the priests, as it says "And you shall speak to the Levites and say to them: When you take from the children of Israel the tithe that I have given you from them as your inheritance you shall lift up from it a heave-offering to Ha-Shem, a tithe of the tithe... and you shall give it to... the priest"³; or an Israelite can give the tithe of the tithe directly to the priest.) A second tithe of the remainder is set aside to be eaten in Jerusalem (or to be redeemed and the proceeds spent for food to be eaten in Jerusalem), as it says "You shall tithe all the produce of your crops... and shall eat before Ha-Shem your G-d in the place that he shall choose"⁴; and it says "[And all the tithe of the land... is Ha-Shem's;] and if a man redeems any of his tithe he shall add a fifth to it".⁵ This is done in the first, second, fourth and fifth years of the sabbatical cycle; in the third and sixth years the second tithe is given to the poor instead; while in the sabbatical year no heave-offerings or tithes are set aside in the land of Israel. It is forbidden to set aside these offerings in the wrong order, as it says "You shall not delay your increase or your flowing".^6,a

The commandments regarding heave-offerings and tithes apply only to the land of Israel, but the prophets and the sages extended them to neighboring lands.^b They apply only to crops that have owners and are used for human food; they also apply rabbinically to vegetables.^c Even priests and Levites must set aside the offerings and tithes, as it says "So you too shall lift up the heave-offering to Ha-Shem"³; but if they themselves are entitled to them they need not give them to others.^d

b) Use of the Offerings

The offerings that are given to priests can be used only by priests, their families and their property. They are forbidden to non-priests even if they are employed by priests, as it says "And no stranger shall eat a sacred thing; a tenant or hired servant of a priest shall not eat a sacred thing".⁷ If the daughter of a priest marries a non-priest she may not eat the offerings; but if she is widowed or divorced and has no living descendant by the non-priest she may eat them, as it says "And if the daughter of a priest becomes [wife] to a strange man she shall not eat of the sacred heave-offerings; but if the daughter of a priest becomes a widow or a divorcee and has no child and returns to her father's house as in her youth she may eat of her father's bread".⁸ Conversely, the wife of a priest may eat the offerings, and even if she is widowed or divorced she may still eat them if she has a living descendant by the priest even if this descendant is not a priest. If a woman has forbidden sexual relations she cannot eat the offerings. A priest who is impure cannot eat the offerings, as it says "If any man of the children of Aaron is impure he shall not eat of the sacred things..."⁹; nor can an uncircumcised priest eat them.^e

If one who is forbidden to do so uses the offerings he must pay 5/4 of their value, as it says "And if a man eats a sacred thing in error he must add a fifth to it and give the sacred thing to the priest".¹⁰ Even a priest may use the offerings only for eating, drinking, or anointing (or if they are impure, for burning). It is forbidden to make the offerings in the land of Israel impure.^f

Sources:
1. Deut. 18:4	a. Matnos Aniyim 6:2-6; 3:1-2,12,23
2. Num. 18:21,24	b. 1:1 (and see 1:26)
3. Num. 18:26,28	c. 2:1,6
4. Deut. 14:22-23	d. Maaser 1:3-4
5. Lev. 27:30-31	e. 6:1,3,5,7-8,10,12-14; 7:1,10
6. Ex. 22:28	f. 10:1; 11:1; 12:1; see 7:3. On the "fifth" see Shevuos, Note c.
7. Lev. 22:10
8. Lev.22:12-13
9. Lev. 22:4-7
10. Lev. 22:14