Apple is correct. The -ing form of a verb сan be used as a noun; it is then called a gerund. A gerund noun like all nouns can be an object or a subject. In your sentence, "I look forward TO hearING from you," hearing is a gerund and the object of the preposition "to". Examples of gerunds as objects of prepositions. She talks "about" going to France. I'm used "to" eating rice with my fish. I'm interested "in" buying the new Beatles album. Would you object "to" my smoking while we talk? If you rewrote your sentence the gerund noun also could be the subject. Example: Hearing from you is what I look forward to... You can learn about gerunds here: http://www.englishclub.com/grammar/verbs-gerunds_1.htm Денис

Actually, the problem here is not the use of an infinitive "to". It is that all of the prepositions (including "to" here) are part of phrasal verbs: "to look forward to" "to talk about" "to be fond of" etc. And, after these, a gerund object (like "hearing") is the same as it would be if the verb were not phrasal: Ex.: "I highly anticipate hearing from you."

'to+verb ' , as far as i know ,it belong to infinitive verb, which is stiplulated in grammer. to +verb-ing ， when the verb is followed a Preposition we must add the -ing in the end of verb.thus the verb turn to noun, we know preposition must combine with noun or pronouns.

I agree with apple. the "to" in the sentence 'look forward TO hearING from you', acts as preposition and that the verb followed by it should end in 'ing' form. other prepositions such as 'in', 'on', 'at', 'with', 'from', are always followed by the -ing form rather than infinitive. "I look forward TO meeting you soon!" "Please refrain FROM opening the box." :)