Fishbone Diagrams also referred to as cause and effect diagrams, are a problem solving and fault finding tool which dissect an issue or problem into a standard four contributing sources approach. Fishbone diagrams get their name from their close resemblance to fish bones. The main horizontal line or “backbone” carries the problem statement, and the diagonal lines on either side of this line pointing towards it represent each of the contributing sources from which other lines stem representing possible causes or hypothesis. The four contributing sources to a problem or issue used in a fishbone diagram are:

-Machinery and equipment
-People
-Materials
-Methods

For an example of a worked fish bone diagram: Fish bone diagram example

These sources then allow the user to further drill down into possible root causes relating and surrounding that source. Once the fishbone diagram is complete and all possible causes regarding each source have ben recorded, the individual causes or hypothesis are tested to see if they are valid causes. This process should then lead to one or a few actual causes of the problem.
Below is a representation of a fishbone diagram: