Millions of people around the world communicate better thanks to Mignon Fogarty, aka Grammar Girl, whose top-rated weekly grammar podcast has been downloaded more than 40 million times. Now she's turning her attention to solving your worst problems—one troublesome word at a time.

Are you feeling "all right" or "alright"? Does "biweekly" mean twice a week or every two weeks? Do you run a gauntlet or a gantlet? Is a pair of twins four people or two?

The English language is always changing, and that means we are left with words and phrases that are only sort of wrong (or worse, have different definitions depending on where you look them up). How do you know which to use? Grammar Girl to the rescue! This handy reference guide contains the full 411 on 101 words that have given you trouble before—but will never again.

Full of clear, straightforward definitions and fun quotations from pop culture icons such as Gregory House and J. K. Rowling, as well as from classical writers such as Mark Twain and Benjamin Franklin, this highly-useable guidebook takes the guesswork out of your writing, so you'll never be at a loss for words again.