These are very comfortable and really don't need any break in.
If you wear heavy socks you may need to get 1/2 size bigger.

I wouldn't catagorize these boots as boots. They are more like the spawn of some hi-tech shoes and a tank. They have a sole that is a lot thinner and a rise around the ankle that is a lot shorter than almost all of the hiking boots i've owned or tried on. But this is exactly what I was looking for because it allows me to feel the terrain under my feet and the lower rise doesn't lock in as much heat as taller rising boots. The tank part of these "boots" comes in when I talk about the outer leather and the hardcore rubber surrounding the boot. I beat the heck out of these things and NOTHING happens to them. With all of that toughness on the outside one would think these hand out a new blister every mile. Well I am happy to say that that does not happen and that these are the most comfortable boots that I have ever owned in my life. They fit my feet sooo perfectly. Maybe I just got lucky but it is like they were made for my feet, they feel like an extension of my body instead of a boot that I take on and off, haha. My feet do sweat like mad in these but my feet sweat like mad even in sandles so I am not holding that against Merrel. I wear size 11.5 and they are perfect. To give you guys some comparisons I wear size 11 Nike running shoes, size 10.5 La Sportiva climbing shoes, size 10 Vasqe hiking boots, and size 11 Speedo water shoes. I love these "boots"!!!