The chasuble is the outermost liturgical vestment worn by clergy for the celebration of the Eucharist in Western-tradition Christian Churches that use full vestments, primarily in the Roman Catholic Church, in "high church" and "broad church" Anglican congregations, and in some parts of the United Methodist and Lutheran Churches. It is also used as the primary Eucharistic vestment in many Lutheran parishes (see Apology of the Augsburg Confession, Article XXIV). In the Eastern Churches of Byzantine Rite, the equivalent vestment is the phelonion.
"The vestment proper to the priest celebrant at Mass and other sacred actions directly connected with Mass is, unless otherwise indicated, the chasuble, worn over the alb and stole" (General Instruction of the Roman Missal, 337). Like the stole, it is normally of the liturgical colour of the Mass being celebrated.
The chasuble originated as a sort of conical poncho, called in Latin a "casula" or "little house," that was the common outer traveling garment in the late Roman Empire. It was simply a roughly oval piece of cloth, with a round hole in the middle through which to pass the head, that fell below the knees on all sides. It had to be gathered up on the arms to allow the arms to be used freely.
As the casula became a liturgical garment in the West, it was folded up from the sides. Strings were sometimes used to assist in this task, and the deacon could help the priest in folding up the sides of the vestment. Beginning in the thirteenth century, there was a tendency to shorten the sides a little, as can be noticed in the illustration here of a fifteenth-century chasuble. In the course of that fifteenth century and the following century, the chasuble took something like the modern form, in which the sides of the vestment no longer reach to the ankle but only, at most, to the wrist, making folding unnecessary.
At the end of sixteenth century the chasuble, though still quite ample and covering a little of the arms, had become less similar to its traditional shape than to that which prevailed in the nineteenth and early twentieth centuries, when the chasuble was reduced to a broad scapular, leaving the whole of the arms quite free, and was shortened also in front and back. To make it easier for the priest to join his hands when wearing a chasuble of stiff (lined and heavily embroidered) material, the front was cut away further, giving it the distinctive shape often called "fiddleback". Complex decoration schemes were often used on chasubles of scapular form, especially the back, incorporating the image of the Christian cross or of a saint; and rich materials such as silk, cloth of gold or brocade were employed, especially in chasubles reserved for major celebrations.
In the twentieth century, there was a tendency to return to an earlier, more ample, form of the chasuble, sometimes called "Gothic", as distinguished from the "Roman" scapular form. This aroused some opposition, as a result of which the Sacred Congregation of Rites issued on 9 December 1925 a decree against it, which it explicitly revoked with the declaration Circa dubium de forma paramentorum of 20 August 1957, leaving the matter to the prudent judgement of local Ordinaries. There exists a photograph of Pope Pius XI wearing the more ample chasuble while celebrating Mass in Saint Peter's Basilica as early as 19 March 1930.
After the Second Vatican Council the more ample form became the most usually seen form of the chasuble, and the directions of the GIRM quoted above indicate that the beauty should come from its drapery and form rather than elaborate decoration ("fiddleback" vestments were often extremely heavily embroidered or painted with detailed decorations or whole scenes depicted). Hence, the prevalence today of chasubles that reach almost to the ankles, and to the wrists, and decorated with relatively simple symbols or bands and ophreys.
Some see a preference for the "fiddleback" as a sign of traditionalism or even rebellion against the reforms of the Second Vatican Council. However, some priests express simply on grounds of taste and comfort a preference for the scapular form, which continues to be included in mainstream catalogues of liturgical vestments; and other traditionalist priests prefer, for similar reasons, ampler chasubles of less stiff material.