It’s possible that some of us have a vague idea at the back of our brains that you shouldn’t use a comma before and. I know that sometimes this was taught as a punctuation rule in UK schools. But punctuation is intended to make things clear and to be an aid to reading, not a set of hard and fast rules, and should is a word I dislike intensely and try to avoid if I can. There are certainly some situations where a comma before and is preferable and helpful.

Oxford comma (sometimes called serial comma)

This refers to a comma before the final and in lists; so called because it was traditionally used by Oxford University Press. There is some disagreement about it. Some people include a comma in a series or list of three or more:

• He ate ham, eggs, and chips.

In my opinion, in straightforward lists, a comma is not needed:

• He ate ham, eggs and chips.

But sometimes a comma is useful in a list to make things clear:

• My usual breakfast is coffee, bacon and eggs, and toast.
• I dedicate this book to my parents, JK Rowling, and Terry Pratchett.

In the first example, the comma before the final and makes it clear that the eggs accompanied the bacon rather than the toast.

In the second example, without the comma before the and, you might conclude that my parents were JK Rowling and Terry Pratchett.

Comma before and used as a conjunction:

When and is used to connect two independent standalone clauses, a comma is often used:

• The rain stopped, and the sun came out again.
• It is nearly half past seven, and we cannot reach London before dark.

When and is used to connect a dependent clause to a main clause, a comma is seldom used:

• The boy hit his thumb with a hammer and cried.
• She trained hard and won the race.