What is the difference between contractor and subcontractor?

Here's the idea.

I give you a contract to build a house for me. You give Fred a contract to do the roof, and Mary a contract to do the walls.

You are the main contractor. You work for me.

Fred and Mary are subcontractors. They work for you.

The prefix 'sub' means 'under'. Fred and Mary work 'under' you, ie 'under' your contract.

Teachers: We supply a list of EFL job vacancies
if im a sub do i need a contractor to do the work
Who do you have a contract with?
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This was incredibly helpful! Thank you!