If you are looking to buy a license today, you have two main paths: 1. One-Time Purchase (Perpetual) You pay once and own that specific version forever.
You pay a monthly or yearly fee for the most current features and extra perks. buy windows office 2015
If you tell me what you'll be (e.g., personal use, school, or a small business), I can help you pick the most cost-effective version for your needs. If you are looking to buy a license