It depends on the type of loan you will be using.
Both FHA and Conventional (on good credit) will loan 97% of purchase price. Sometimes you can get a second loan to pay 2.5% of the purchase price which leaves you with .5% of purchase price to cough up for a down payment. Earnest money can go toward a down payment as well.
If you pay anything less than 20% of the purchase price toward a down payment, you will have to pay a monthly mortgage insurance (MI). This can drop once you have 20% equity of the property.
This will have to be applied for and you will have to pay an appraisal fee.
Some loans will drop the MI once you reach 22% loan to value, so speak with your lender on this.