to the best of my knowledge

To the best of my knowledge is a phrase which means as far as I know. This is another way of saying that with all of the knowledge you currently possess about this particular subject, then what was just said to you must be true. It is usually a phrase which is followed by a fact of some kind. When you say, for instance, to the best of my knowledge that is how it happened then you are trying to make a point that you think that happened, as far as you are aware of.