Canning tomatoes is a process of preserving tomatoes by packing them in jars or cans and then boiling them. This method of preservation has been used for centuries, and is still popular today. The most common type of tomato used for canning is the Roma tomato, which is a small, round tomato with a thick skin and low acidity. Canning tomatoes is a great way to store tomatoes for long periods of time, and it also helps to retain their flavor and nutritional value.