Most essential oils are distilled but other extraction methods are used, especially for botanicals that would be chemically altered by the heat produced during distillation.
Most essential oils are made from a specific plant part. Sandalwood, for example, is made from the wood of a tree. Angelica, on the other hand is distilled only from the roots of its parent plant. Other essential oils, like lavender, are distilled from flowers; citrus oils are produced by pressing the rinds of ripened fruits.