In computing, logging is the act of keeping a log of events that occur in a computer system, such as problems, errors or just information on current operations. These events may occur in the operating system or in other software. A message or log entry is recorded for each such event. These log messages can then be used to monitor and understand the operation of the system, to debug problems, or during an audit. Logging is particularly important in multi-user software, to have a central overview of the operation of the system.

In the simplest case, messages are written to a file, called a log file. Alternatively, the messages may be written to a dedicated logging system or to a log management software, where it is stored in a database or on a different computer system.

Specifically, a transaction log is a log of the communications between a system and the users of that system, or a data collection method that automatically captures the type, content, or time of transactions made by a person from a terminal with that system. For Web searching, a transaction log is an electronic record of interactions that have occurred during a searching episode between a Web search engine and users searching for information on that Web search engine.

Many operating systems, software frameworks and programs include a logging system. A widely used logging standard is Syslog, defined in Internet Engineering Task Force (IETF) RFC 5424). The Syslog standard enables a dedicated, standardized subsystem to generate, filter, record, and analyze log messages. This relieves software developers of having to design and code their ad hoc logging systems.