The house edge in European roulette is 2.7%. This percentage represents the advantage that the casino has over players, meaning that for every bet placed, the casino is expected to retain 2.7% of the total amount wagered in the long run. This edge arises from the presence of a single zero on the wheel, which distinguishes European roulette from its American counterpart, which has both a single and a double zero, resulting in a higher house edge.