hearing I'm adding to this because so many people are answering incorrectly: after a verb + preposition, you must use the gerund form (ing) See the link below: http://www.ego4u.com/en/cram-up/grammar/infinitive-gerund/wordlist?24

look forward to +v(ing) or a noun i look forward to hearing from you. i'm looking forward to going on vacation. i look forward to the summer holiday.

This depends on the context in which you are using this phrase: 'hear' as a verb (used without an object) (As steve mentioned you will need ing after verb + preposition): I look forward to hearing from you. 'hear' as a verb (used with object) To hear what is being said you will need to pay attention.

the correctanswer is TO HEAR.. for example the verb ''to hear''.i want to her you sing or inorder to hear.Hearing is a continuous action and as such we dont use to with a continous action.

I look forward to hear from you.