We could not have been happier with Yellowstone Adventure Tours. Derek, the owner, runs the business expertly and, prior to our trip, was very responsive to all our questions. He also communicated quickly and clearly the changing situation when Yellowstone was closed due to flooding. Our two-day tour of the lower loop was perfectly paced and so much fun. Our guide, Kevin, was outstanding. We have employed guides and guide services at other national parks and on excursions of one kind or another. Kevin is the best of the best. Personality-wise, he is easy-going and very friendly. He wants to know what your top interests are and will shape the itinerary to achieve what you like, including how early to start, how hard to push, how strenuous hikes are, etc. As a scientist (biologist), he is very knowledgeable in a way that is much deeper than book-deep or just memorizing facts (as some guides do). He is thoughtful, cares for your personal safety and your intellectual engagement, and truly knows the park, its history and mysteries, and will show you simply extraordinary views, topologies, geologic phenomena, and the big animals. I understand that many people are hesitant to engage a guide who they do not know, but Kevin is the kind of person who you will feel you have known for 10 years within an hour of meeting him. We did a 2-day tour with Kevin, starting at 6:30 each day, and we learned so much, had so many great experiences, and really fell in love with Yellowstone because of his guidance and support. We give Kevin, Derek, and Yellowstone Adventure Tours our HIGHEST possible recommendation.