While surfing the Web yesterday, I stumbled upon a question asked by one curious person. The question was about the difference between two very similar words: inquire and enquire. The author of the question seemed to be very eager to learn the distinguishing characteristics of the two terms. It turns out, however, that the two words mean the exact same thing and can be used interchangeably. There are some things, however, one needs to bear in mind while using the words either in the written or the oral form.
First of all, inquire seems to be the more popular form of the word, so if you want to play it safe, you will stick with this version of the word.

Secondly, enquire seems to be more popular in the British English while inquire seems to be more common in the US. This fact didn’t prevent the editors of the Oxford English Dictionary from recognizing inquire as the more dominant form while deeming enquire at the same time.

The bottom line is the following: use inquire unless somebody specifically asks you to use the other version of the word. End of story.