It has become a popular cultural tradition around Christmas time to hear that Christ was born in a manger because there was no room in the inn. However the New Testament mentions neither a manger as we understand it nor an inn when describing the Christmas story. For more details on this topic and possible alternative explanations, I recommend the following articles:
The Manger and the Inn
Away in a Manger, but Not in a Barn
"No Room in the Inn"