Are airplane seats lettered left to right or right to left or does it depend on the airline?

All major airlines letter seats from right to left as you are standing in the aisle facing the rear of the plane. Thus seat “A” is always next to the right window. There are other variations though that do depend on the airline. For example, one airline with 2 seats on the right and three on the left may label them as A and B, and then D, E, and F, while another airline may use A and C, and then D, E, and F.