In computer science, dependency is a state where one object uses a functionality of another object. This may cause changes on implementation of one object can affect that of another object. Supposedly, Information hiding is a way to eliminate dependency to limit influence of changes and improve modularity. Dependencies can be reduced by applying the dependency inversion principle . Examples of dependency relationships are aggregation (is-part-of), inheritance (is-a), subtyping, uses and implements relationships.

It also is common in talking about software package management. One software package, in order to work or to be fully functional, may depend on other software packages and thus must be installed also, and their specific versions must be known if backward compatibility is broken between versions. The Apt package format, as well as some versions of the RPM package format, include dependency information between packages. This is convenient for updating software but can lead to dependency hell.