1. For general points of usage see be. Some common and interesting idiomatic uses of is are given here.
2. For is after a compound subject, as in Fish and chips is my favourite meal, see agreement 3. For problems of agreement between subject and complement when one is singular and the other is plural, as in More nurses is the next item on the agenda, see agreement 5.
3. is what…or…is how…following a statement.

• One never knows with these lefties, is what I always say —A. Brink, 1988

• You step up to him and you cart him all over the park, is what you do —S. Fry, 1990.

This use, as the contexts of these examples show, is highly informal.
4. is nothing to do with.
This construction, as an alternative to has nothing to do with, was defended by Fowler (1926) as the more natural choice in everyday speech ‘when we…are not in the mood for weighing words in the scales of grammar’, is found in the 19c

• (This is nothing to do with your life —H. S. Merriman, 1896)

but is less common than the construction with have in current use to judge by the evidence in the British National Corpus and in the OED.
5. is —.

• Let anyone repeat, as often as he pleases, that ‘the will is the will’ —Locke, 1690

• A man's a man for a' that —Burns, 1790

• Home is home though it is never so homely —Charles Lamb, 1823.

These older literary uses are echoed in 20c occurrences:

• A job's a job, that was the thing —Maurice Gee, 1985

• She worried about Colin's wrist in the cast but a trip out was a trip out, and the day mustn't be spoiled —N. Virtue, 1990.

Occasionally the word is is repeated (echoing Gertrude Stein's

• Rose is a rose is a rose is a rose, is a rose… —Sacred Emily, 1913)


• There is only one art form common to all sorts and conditions of people: the poster…A hoarding is a hoarding is a hoarding —Guardian, 1970.

6. postponed and repeated is.
This somewhat informal use dates from the early 19c:

• He's a sad pickle, is Sam! —M. Mitford, 1828

• Yes, he is true to type, is Mr Heard —Ronald Knox, 1932.

7. is all.

• No one's interested, is all —M. Doane, 1988.

This idiomatic expression, used for emphasis at the end of a sentence, sounds dialectal but is found in standard (especially American) works of fiction.

Modern English usage. 2014.