The Amish (followers of Mennonite factionalist Jacob Amman) subscribe to a theological position called Anabaptism which holds that baptism can only be received by a reasoning, consenting adult. This belief originated at a time when infant baptism, performed by church officials, was the norm. The distinction between sixteenth-century church and state being tenuous at best, rejection of infant baptism was thus understood as a rejection of state power. This has meant persecution for much of their history.
The popular impression of this people is that they live the way they do because of "religious codes." Not exactly. They have religious codes, sure enough, but they're about rejection of war, sanctity of marriage, adult baptism, etc. Over the centuries, certain of these codes have gotten them in hot water with various authorities. So they have developed a strong ethic of in-group solidarity as well. And it is this solidarity which explains their way of life or, more accurately, their way of making a living.
Although always quirky, the Amish up until about the American civil war lived much the same way as everybody else. Think about it; they don't use the technology of the sixteenth century, which is roughly when they emerged as a sect. They use the technology of the nineteenth century. In the late 19th century, the bishops began to see that inventions such as the electric light, the steam engine, and other features of the industrial revolution were going to change the way people related to each other and fragment community life as America had know it up to that point. A persecuted people would not survive fragmentation such as this. So they began to make the rules that most people are familiar with. The evolution of the rules is an interesting history by itself; my personal interpretation is that they are designed, functionally at least, to keep labor and means of capital formation within the community insofar as possible. It's widely known among small farmers that a major enemy of profits is off- farm capital expenses. But the animal-powered farm, or better yet community, has less outlay and less depreciation on that input than does the heavily mechanized farmer or community.
The rules function in other ways as well. It's not feasible for one family to farm huge acreages with the horse. If tractors were allowed in the fields, a given family would naturally be tempted to work more acres and drive their neighbors off the land by buying them out in a bad year. Avoiding these types of community-splitting pressures is part of the rationale for using animal traction. The Amish are occasionally accused of hypocrisy in allowing stationary engines but no moving engines; but if you use a stationary engine to lift silage, for example, the amount of silage you are working is already limited by the restriction on mechanized draft. In such a case, there is no reason not to use the stationary engine.
The political structure and history of the Amish displays their concern and intimacy with the dynamics of collective survival. If you look around today at the battered shells of former farm communities you will see that way back in the late 1800s, the bishops were right. They have hung onto certain material preconditions for liberty that the rest of us have lost. Control over land, labor, and capital, in particular with respect to fuel/food/fiber production, is control over a substantial means of existence. If the Amish can control a large segment of their collective means of existence we should study them closely and take a page from their book, without necessarily committing ourselves to their spiritual precepts or to petit-bourgeois romanticism. I might note at this point that Kropotkin claimed the early Anabaptists as ancestors of anarchist communism, but I take this as more or less a wishful effort at colonizing the past.
Most animal-power farming is done with antique equipment, as one might suspect, but little is left in working order. I find it encouraging that there's enough demand for new production of animal-drawn gear, ranging from harness on up, to be economically feasible. The Amish are in no meaningful sense "anti-technology." In 1994 I saw several pieces of brand new horse-drawn gear from an Amish company called White Horse Machine, one of which is a double-bottomed plow with hydraulic lift, reset, and tongue centering. Energy for this is stored by a ground-driven pump that compresses nitrogen in the oil chamber (as opposed to the more familiar oil-impeller coming off an engine). It's remarkable enough to look at, and yet more so when you recall that these Amish engineers only have an eighth- grade formal education. Their technical prowess is all learned by doing, in an informal but thorough apprenticeship system- another important topic for study.