精炼是将物质进行提纯的过程，主要是指对自然资源中可用的部分进行纯化，使其能更好地被利用。例如天然石油可以直接燃烧，但燃烧后会产生大量的残渣，燃烧不完全。精炼后会得到汽油、柴油、重油、沥青等不同产物，用于不同的用处。广义地讲，精炼也包括对矿物的筛选提炼，例如从矿石中提炼金属等。

对液体的精炼一般使用蒸馏和精馏的方法；对气体要先冷却、压缩产为液体后精馏。对液体和气体的提炼也可以采取萃取的方法，利用某些溶剂溶解需要提炼或需要抛弃的部分。

对固体的提炼可以利用其在某些溶液中结晶的方式，结出的晶体可以排除不需要的杂质。

Refining (also perhaps called by the mathematical term affining) is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it will burn poorly and quickly clog an engine with residues and by-products. The term is broad, and may include more drastic transformations, such as the reduction of ore to metal (for which see Refining (metallurgy)).