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A root cause is an initiating cause of a causal chain which leads to an outcome or effect of interest. Commonly, root cause is used to describe the depth in the causal chain where an intervention could reasonably be implemented to change performance and prevent an undesirable outcome.
In plain English a "root cause" is a "cause" (harmful factor) that is "root" (deep, basic, fundamental, underlying or the like).
The term root cause has been used in professional journals as early as 1905.
Paradies (2005) has defined a root cause as follows: "The most basic cause (or causes) that can reasonably be identified that management has control to fix and, when fixed, will prevent (or significantly reduce the likelihood of) the problem’s recurrence." 
Fantin (2014) describes the root cause as the result of the drill down analysis required to discover which is the process that is failing, defining it as "MIN Process" (meaning a process that is Missing, Incomplete or Not followed)
- Forensic engineering
- Proximate and ultimate causation
- Root cause analysis
- RPR Problem Diagnosis
- Three Unwholesome Roots
- "The Present State of Medical Practice in the Rhondda Valley". The Lancet 166 (4290): 1507. 18 November 1905. doi:10.1016/S0140-6736(00)68499-4.
- Mark Paradies (17 October 2005). "Definition of a Root Cause". Retrieved 28 July 2012.
- Ivan Fantin (2014). Applied Problem Solving. Method, Applications, Root Causes, Countermeasures, Poka-Yoke and A3. How to make things happen to solve problems. Milan, Italy: Createspace, an Amazon company. ISBN 978-1499122282