A BTL Mortgage is a buy to let mortgage. These mortgages are designed for those who want a mortgage for the purpose of letting the property out to tenants.  These types of mortgages have become very popular over the past few years. The rise in popularity is due to the increasing house prices, a strong demand for rental properties and a drop in the interest rates available to private landlords. Many mortgage products are available, this includes fixed rates, discount, tracker and variable rates.