Kilayim, Chapter 8, Mishnah 1. This mishnah lists the various categories of kilayim that are relevant throughout the entire tractate - some of whose details we have already studied, and some of which we have not yet encountered.
Kilei HaKerem (Vineyard Kilayim):
The mishnah opens with the kilayim connected to a vineyard, and there are three halachos regarding them: "asurin mil'zroa umil'kayem, va'asurin ba'hana'ah" - they are forbidden to be sown and to be maintained, and they are forbidden to derive benefit from.
"Mil'zroa" - one may not sow kilayim in a vineyard, and one may not place a foreign growth alongside the vines, together with the grapevines.
"Mil'kayem" - even if the person did not sow it himself, but rather the plant came up on its own, or someone else who is not the owner sowed it against his will - since the situation is under his responsibility, he is not permitted to leave it standing in its place, but is obligated to uproot it.
"Va'asurin ba'hana'ah" - the growth that grew there is forbidden to derive benefit from, and one may not gain any use from it whatsoever. This is a halachah unique to kilei hakerem.
Kilei Zera'im (Seed Kilayim):
From here the mishnah moves on to a mixture of different species of plants or vegetables in which no vineyard is involved: "asurin mil'zroa umil'kayem, umutarin ba'achilah v'chol shekein ba'hana'ah" - they are forbidden to be sown and to be maintained, but they are permitted to be eaten, and all the more so to derive benefit from.
"Mil'zroa" - one may not sow different kinds of vegetables and produce together.
"Mil'kayem" - even if he did not sow them himself, once he comes across them he is obligated to uproot them, and he may not leave them to grow together.
"Umutarin ba'achilah v'chol shekein ba'hana'ah" - despite the prohibition to sow them and to maintain them, eating them is permitted, and it certainly follows that one may derive benefit from them.
Kilei Begadim (Garment Kilayim):
These are the kilayim generally known as sha'atnez - wool and linen mixed together. Regarding them the mishnah rules: "mutarim b'chol davar, v'ein asur ela mil'vushah" - they are permitted in every way, and a person may benefit from them and put them to various uses; the prohibition is only that of wearing them.
Kilei Beheimah (Animal Kilayim):
Regarding a mixture of animals of different species, the mishnah says: "mutarin l'gadel ul'kayem, v'ein asurin ela mil'harbia" - they are permitted to be raised and maintained, and are forbidden only to be crossbred. Two approaches have been offered in understanding these words:
It is permitted to raise two different species together and to maintain them together - to feed them from the same trough and to keep them in the same pen.
Others explain that the mishnah is not discussing what one is permitted to do with two different species of animals, but rather 'kilei beheimah' in the sense of the product of the mating of two different species: the crossbreeding itself is forbidden, but the offspring born from it - such as a mule whose parents were crossbred by others - may be raised and maintained. The prohibition is limited to crossbreeding a donkey and a horse together in order to produce the mule.
The mishnah further rules that kilei beheimah, meaning the products of the crossbreeding of two different animal species, "asurin zeh b'zeh" - are forbidden with one another, both for crossbreeding with each other and for working together. For example, a mule born from a female donkey and a horse as compared with a mule born from a mare and a male donkey: even though both are mules, since they come from two different types of crossbreeding - the mother of one is a mare and the mother of the other is a female donkey - they are considered two different species, and one may not crossbreed them with one another, nor even work them together.
In summary: in this mishnah the mishnah enumerated the categories of kilayim and the halachos that apply to each one: kilei hakerem - forbidden to sow, to maintain, and to derive benefit from; kilei zera'im - forbidden to sow and to maintain, but permitted to be eaten and to be benefited from; kilei begadim - permitted in every way and forbidden only to be worn; and kilei beheimah - permitted to raise and maintain, their prohibition being crossbreeding, and even the products of different crossbreedings are forbidden with one another both for crossbreeding and for working together.