A modular dog kennel can be re-arranged in different ways, to accommodate different needs you and your pets may have. They are often made out of metal, often with panels that can be added on to increase the size of the kennel or change the shape, or partitions that can be added or taken away.

These type of kennels are very useful if you have more than one dog sharing a living area as you can give each of them a place 'of their own' they can retreat to.  They are also particularly helpful when a female dog is about to whelp.  They provide privacy and a place where she can deliver and keep her pups, and other sections where she can get away from them at times to stretch her legs. They are also helpful when teaching the very young pups to move away from their living and sleeping space to eliminate which is a very important lesson for them as it makes it much easier to housetrain the puppies when they're older.

Another reason for investing in a modular kennel is so you can keep pace with your dog's growth.  Puppies are small but they grow, and some dogs can grow quite big. Rather than investing in a big sized kennel right off the bat, you can instead start off small then add to the kennel as the pup grows.  Dogs like their pens and kennels to be cozy and to offer security. Too big can cause them to become insecure. So, start off small and add to it as needed.