Sulfides are natural compounds of sulfur with metals, most commonly with iron, copper, zinc, lead, silver, gold, cobalt, nickel, or metalloids like arsenic, antimony, and bismuth. This class also includes arsenides and tellurides, compounds of the aforementioned metals or metalloids with arsenic or tellurium. There are over 300 different mineral species in the sulfide class, but only around twenty are found in significant quantities.

This class contains many ore minerals with significant economic importance, such as the most important copper ore minerals (chalcosite, chalcopyrite, bornite, and covellite), lead (galena), zinc (sphalerite), silver (argentite), mercury (cinnabar), nickel (niccolite), arsenic (arsenopyrite and auripigment), antimony (stibnite), and molybdenum (molybdenite). Other well-known minerals from this class include pyrrhotite, polymorphs of iron sulfide, FeS₂, pyrite and marcasite, as well as realgar, millerite, and others.

In terms of luster, sulfides were traditionally divided into four categories:

"Pakovine": These have a metallic luster, are opaque, light-colored, and have a black streak, generally harder, without noticeable cleavability, and brittle.
"Sjajnici" (shiny): These have a strong metallic luster, are opaque, usually gray in color with a black streak, softer, and often exhibit perfect cleavability.
"Blistavci" (brilliant): These have a diamond-like luster, are sometimes transparent, are usually softer, exhibit good cleavability, and are brittle.
"Sinjavci" (bluish): These have a metallic luster, dark gray or blue color, and a black streak, are opaque, soft, without cleavability, and brittle.

Sulfides are most commonly found in ore veins of hydrothermal origin, crystallizing from hot aqueous solutions from deep within the Earth's crust. They can also form sedimentarily under reducing conditions.