Meryn Stol voted up this answer. Darrell Francis It really depends on the person. For most decent writers, it's pretty much impossible to tell a native speaker from a non-native speaker. There might be subtle clues, such as uncommon word choices, but what they write is correct even if it sounds a little awkward to a native speaker. The thing to look for is mistakes in the writing. Native English speakers also make mistakes, but the mistakes they make are different than the ones non-native speakers make. Misspellings are a bad clue as they could just be a typo and anyone could make that mistake. One telling mistake are homophones, words which sound alike, but have different spellings. A native speaker is more likely to confuse "your" and "you're" because it sounds correct and they aren't thinking about grammar. A non-native speaker doesn't have that innate sense of what "sounds correct", therefore they're less likely replace a word with a homophone. For example, I just saw a question... - Meryn Stol