Custom software is software that is specially developed for some specific Company,Human being.It can be contrasted with the use of software packages developed for the mass market.

Custom software can be developed by a software development company, or be commissioned by a independent software developer.

Since custom software is developed for a single customer it can accommodate that customer's particular preferences and expectations. Custom software may be designed in stage by stage processes, allowing all possible hidden dangers to be taken into account, including issues which are not mentioned in the specifications. Especially the first phase in the software development process may involve many departments, including marketing, engineering, research and development and general management.

Large companies commonly use custom software for critical functions, including content management, inventory management, customer management, human resource management, or otherwise to fill needs that existing software packages cannot. Often such software is legacy software.