動詞不定式做後置定語就是不定式位於被修飾詞的後面充當定語。例如，the house to live 用來住的房子 。

當作定語的成分放在被修飾的詞之前時，叫做前置定語。

當作定語的成分放在被修飾詞之後時，就叫做後置定語。

當動詞不定式作定語修飾名詞或者代詞時通常要放在被修飾詞之後作後置定語。例句：

1.I have much work to do every day.

2.There is nothing to worry about.

3.Tom has no chair to sit on.

除不定式作定語後置外，形容詞修飾複合不定代詞、副詞(here, there)、介詞短語、分詞短語、定語從句等作定語時通常都要後置。

動詞不定式作定語後置表示要做的事尚未發生，常與名詞有動賓關係：

He has lots of things to do.

Jack needed someone to carry the box.

She always the first one to arrive at the school.

There are a lot of things to do.

The boy to be sleeping in the room is my younger brother.

The building to have been built is our teaching building.

The person to have been watching TV in the room is my father.

動詞不定式放在名詞的後面修飾這個名詞就叫後置定語，通常晚於謂語動詞發生。例如：The trees to be planted next year are orange trees.有待明年去種的樹是橘子樹。 再如：The problem to be discussed at the meeting in a minute is about medicine. 過會在會上討論的問題是有關醫學的。