The definitive source of information on Scrum. Frequently revised and updated based on feedback. The last update included an expanded view of the Scrum Values.
Bottom line if you are saying that you do Scrum, and haven't recently read the Scrum Guide then you are probably 1) misinformed 2) out of date. The guide does not go into a lot of detail on the specific practices to used - it is assumed ideas for these can be found in other places - but does provide the absolute essentials. While it appears simple, you will find there is a lot more to it than the words seem to capture.