From the sources . . . .
A man's honour is in his clothes.
Shmot Rabbah 18:5
The garment on which a person is obliged by Torah law to put tzitzit is one which has four or more corners. Its size must be such that it can cover the head and most of the body of a child who is old enough to go on his own to the market, without needing someone else to watch him or walk with him ["And it seems that this would be a child of about six or seven years of age" - Sefer Hachinuch, mitzva 386]. The garment should be of wool or of linen.
Rambam, Hilchot Tzitzit 3:1
A garment made from other fabrics . . . is only obliged to have tzitzit by Rabbinic law (d'rabanan), in order to alert us to the importance they attach to the commandment (mitzva) of Tzitzit . . .
Rambam, Hilchot Tzitzit 3:2
What is the obligation of the commandment of tzitzit? Any person who is obligated to fulfill this commandment, if he covers himself with a garment that is appropriate for tzitzit, he should put in tzitzit and only then cover himself with it . . . However, garments that would require tzitzit - if they are not worn, but folded and stored away, they are exempt from having tzitzit, since [tzitzit] is not an obligation of the garment, but rather of the person [wearing] the garment.
Rambam, Hilchot Tzitzit 3:10
That you should remember all the commandments of the Lord Bamidbar (Numbers) 15:40 - Since the numerical value of the word Tzitzit is 600, and together with the eight stands and five [double] knots, the total is 613 [the number of commandments in the Torah].
Rashi on Bamidbar (Numbers) 15:39
. . . but the remembrance is through the strand of techelet . . . as it says (Menachot 43b), "techelet is like the [color of the] sea, and the sea is like the sky and the sky is like the Throne of Glory, etc."
Ramban on Bamidbar (Numbers) 15:38
What makes techelet different from all the other colors, so that God commanded that it be added to the tzitzit? It is because techelet is like the [color of] grass, and grass is like the sea, and the sea is like the sky, and the sky is like the rainbow, and the rainbow is like the cloud, and the cloud is like the [Divine] Throne, and the Throne is like His Glory . . . and He granted [the mitzvah that includes] techelet to those that fear Him . . . .
Bamidbar Rabbah 14:3
The size of a garment that requires tzitzit is such that it would
cover -- length and width -- the head and most of the
body of a child [a] who is old
enough to go to the market alone without supervision,
Shulchan Aruch (16:1)
[a] of a child: aged 9 years.
[b] requires tzitzit: An adult who wears a garment of this size would have to put tzitzit in it. This is to exclude the case of a garment that is smaller than the specified size, which all authorities agree would be exempt from having tzitzit, even if an adult (see [c] below) might wear it occasionally to go out to the marketplace. However, if all the people of that place would not be embarrassed to wear such a garment regularly when going to the marketplace, then [a garment of that size] would require tzitzit [Bach].
[c] an adult: i.e. 13 years old.
[d] to the marketplace: or, to the front door of the house, facing the street. However, if an adult would be embarrassed to wear such a garment, even on occasion, to go out to the market, then it would not be considered a garment, even if he wears it within his house. There are those who disagree, and they hold that all that is required [for the obligation of tzitzit] is the minimum size. However, the latter authorities [Acharonim] agree that no blessing should be said on such a garment if an adult would be embarrassed to go out with it occasionally . . . And the custom of righteous people is to make a talit katan of one cubit in front and one cubit in length, exclusive of the neck . . . [the Mishnah Berurah here discusses certain local customs of a very small talit katan] . . . But one who fears heaven should not rely on these [approaches] at all, but make for himself a proper garment, each country according to its own custom. And in some places it is customary for a garment called a "camisole" or "vest" to be open at the back, and people put tzitzit on the four corners, and this is commendable; however, they should ensure that the majority of the garment is open [to create four corners], and this also applies to the talit katan made in our own country.
The above is a selection of halachot from various poskim discussing different aspects of the mitzva of tzitzit (tzitzes). It is by no means meant to be a definitive guide, nor replace your local rabbi, who should be consulted on all aspects of halacha, including the halachos of tzitzes.
We hope to be adding to this page in the near future, and would greatly appreciate information, ideas and comments.
The texts were translated by Peretz Zamek.