Oil painting is a type of painting that uses pigments ground into a medium of oil. This "oil paint" is a slow-drying paint consisting of small particles of the pigment that are suspended in drying oil. Currently, many artists hold oil paint in esteem, valuing it as one of art's fundamental parts.

When exposed to air, vegetable (organic) oils oxidize into a dry solid, a process which can be very slow. Though most oils become dry to touch in a day or a few weeks, it can generally be varnished only after six months to a year. You might consider this extreme, but art conservators consider an oil painting to be completely dry only if it has aged 60 to 80 years.

There is a variety of oils that can be used for oil painting, and these lend various unique properties to the paint, such as yellowing. Different types of oil can also differ in their drying times. Beginning from early modern Europe up to present times, linseed oil is the most commonly used carrier oil. It is a relatively expensive oil obtained by crushing the seeds of the flax plant; extracting the oil itself either uses heat, steam, or cold-pressing processes. Other carrier oils include the hemp seed oil, poppy seed oil, walnut oil, safflower oil, and soy bean oil.

In modern times, additives can be added to various organic oils listed above; these are often used to improve the oil's chemical properties. Such characteristics include having faster drying times, varying levels of gloss, resistance to UV, and suede-like finishes. There are also water-soluble oils that can be used with and cleaned up with water, and heat-set oils that remain liquid until heated to 265-280 degrees Fahrenheit.

The oil paint's color borrows from the pigment particles mixed with the carrier oil. For most of oil painting history, natural pigments such as mineral salts and earth types have been used. Examples of natural pigments are lead, zinc, titanium, cadmium, sienna, and umber. In recent times, synthetic pigments have become popular as they widen the spectrum available to painters.

Many natural pigments are toxic and pose a danger to the painter's health. One reason that they are still being used is that many such pigments possess unique properties that somehow offset (in the mind of the artist) the health risk. Examples of toxic pigments still in use for oil paints are lead carbonate (used for some white colors), cobalt (cerulean blue), and cadmium (some red and yellow hues).