Why Does the Transaction Log Keep Growing or Run Out of Space?

Question

This one seems to be a common question in most forums and all over the web, it is asked here in many formats that typically sound like this:

In SQL Server -

• What are some reasons the transaction log grows so large?
• Why is my log file so big?
• What are some ways to prevent this problem from occurring?
• What do I do when I get myself on track with the underlying cause and want to put my transaction log file to a healthy size?