It’s rare, but becoming more common. Established companies will invest in start-ups within their industry (rather than buying them out later).

Generally, you will have to at least have got to the Venture Capital stage, but sometimes these companies will look at ideas in an earlier stage.

However, given the difficulties of such transactions, it is better to have positioned yourself as well as you can before aiming for such a target. So by and large you should have at least raised Venture Capital Funding.