Fits from birth to 35+ lbs. We added special leg gussets to help keep everything in, adjustable rise with four settings, and overlapping closure in both snap and hook & loop. This is a very trim fitting diaper so please be extra careful that none of the insert is sticking out of the shell. Also, after the diaper is on, pull the leg gussets out around baby's legs. This will guard against leaks and help avoid any red marks.