Pastel is an art medium in the form of a stick, consisting of pure powdered pigment and a binder. The pigments used in pastels are the same as those used to produce all colored art media, including oil paints.
"Pastel" is also used:

as a noun – to mean a pastel artwork
as a verb – to represent the process of producing an artwork
as an adjective – to mean a pale color. Pastel media
In order to create hard and soft pastels, pigments are ground into a paste with water and a gum binder and then rolled or pressed into sticks. The name "pastel" from the Italian pastello, meaning "little bread roll". The French word pastel first appeared in 1675.
Most brands produce gradations of a color, the original pigment of which tends to be dark, from pure pigment to near-white by mixing in differing quantities of chalk. This mixing of pigments with chalks is the origin of the word "pastel" in reference to "pale color" as it is commonly used in cosmetic and fashion venues.
A pastel is made by letting the sticks move over an abrasive ground, leaving color on the grain of the paper, sandboard, canvas etc. When fully covered with pastel, the work is called a pastel painting; when not, a pastel sketch or drawing. Pastel paintings, being made with a medium that has the highest pigment concentration of all, reflect light without darkening refraction, allowing for very saturated colors.

Manufacture
Pastel supports need to provide a "tooth" for the pastel to adhere and hold the pigment in place. Supports include:

laid paper (eg Ingres; Canson Mi Teintes)
abrasive supports (eg with a surface of finely ground pumice or marble dust) Pastel supports
Pastels can be used to produce a very permanent form of art if the artist has given appropriate consideration to archival considerations. This means:
Glassine (paper) is used by artists to protect artwork which is being stored or transported. Some good quality books of pastel papers also include glassine to separate pages.

pastels use only lightfast pigments. Pastels which have used pigments which change color or tone when exposed to light have suffered the same problems as can be seen in some oil paintings using the same pigment.
works are done on an acid free archival quality support. Historically some works have been executed on supports which are now extremely fragile and the support rather than the pigment needs to be protected under glass and away from light
works are properly mounted and framed under glass in a way which means that the glass does not touch the artwork. This avoids the deterioration which is associated with environemntal hazards such as air quality, humidity, mildew problems associated with condensation and smudging.
Fixatives — Some artists protect their finished pieces by spraying them with a fixative. Abrasive supports avoid or minimize the need to apply fixative. A pastel fixative is an aerosol varnish which can be used to help stabilize the small charcoal or pastel particles on a painting or drawing. However, fixative will dull and darken pastel's beautiful colors. It is also toxic, therefore it requires careful use. It cannot prevent smearing entirely without dulling and darkening the beautiful colors of pastels. For this reason, some pastelists avoid it's use except in cases where the pastel has been overworked so much that the surface will no longer hold any more pastel, The fixative will restore the "tooth" and more pastel can be applied on top. It is the tooth of the painting surface that holds the pastels not a fixative. Pastels must be framed under glass to prevent damage. Protection of pastel artworks
There are a number of pastel societies around the world.
The Pastel Society in the UK was founded in 1898 and founder members and early exhibitors included Brangwyn, Degas, Rodin, Rothenstein, Whistler and G.F. Watts. Current members are typically professional pastel artists. Admission to membership is via jury selection of artwork for the annual exhibition and agreement of existing members. Signature status is designated by the initials PS.
By way of contrast the oldest pastel society in the USA is the Pastel Society of America - founded in 1972 by Flora Giffuni to promote pastel art and its development. Membership is by jury selection and signature status is designated by the initials PSA.
The International Association of Pastel Societies was founded in 1994 by Urania Christy Tarbet with the aim of promoting pastel art. Its membership is limited to existing pastel societies.

Pastel societies
The pastel medium was first mentioned by Leonardo da Vinci in 1495.
During the 18th century the medium became fashionable for portrait painting, used in a mixed technique with gouache.
In the USA, initially pastels only had occasional use in portraiture. However in the late nineteenth century, pastel (like watercolor) became more popular. The Society of Painters in Pastel was founded in 1885.
Pastels have become popular in modern art due to the medium's broad range of bright colors.
A new Pastel Society has been formed in The Netherlands by Dick Stolp. See www.pastelschilderen.nl/society