A beverage container having a slidably openable lid assembly is disclosed. The lid assembly basically comprises a base member and a cover member. The base member includes a wall portion releasably securing the lid assembly to the container and an opening in fluid communication with a beverage holding chamber in the container. The cover member is slidably coupled to the base member to slide from a closed position to an open position and vice versa. When the cover member is in the closed position it isolates the opening and the contiguous portions of the base member from the ambient surroundings. When the cover member is in the open position it exposes the opening to enable a user to drink the beverage via the opening. The cover includes an elastomeric member arranged to engage and seal the opening in the base member when the cover member is in the closed position.