In economics, an agent's preferences are said to be weakly monotonic if, given a consumption bundle , the agent prefers all consumption bundles that have more of every good. That is, implies . An agent's preferences are said to be strongly monotonic if, given a consumption bundle , the agent prefers all consumption bundles that have more of at least one good. That is, and imply .

This definition defines monotonic increasing preferences. Monotonic decreasing preferences can often be defined to be compatible with this definition. For instance, an agent's preferences for pollution may be monotonic decreasing (less pollution is better). In this case, the agent's preferences for lack of pollution are monotonic increasing.

Much of consumer theory relies on a weaker assumption, local nonsatiation

Local nonsatiation

The property of local nonsatiation of consumer preferences states that for any bundle of goods there is always another bundle of goods arbitrarily close that is preferred to it....

.

An example of preferences which are weakly monotonic but not strongly monotonic are those represented by a Leontief utility function.