The paper will first review how visible sidestream smoke reduction can be evaluated, either during puffing or during smouldering, and expressed on an amount of "tar" per cigarette basis or on a rate of generation basis. Different results can be expected if puff number varies. We will then review the three main mechanisms by which sidestream smoke can be reducted: either modifying mass balance by reducing the amount of tobacco burnt between puffs, or by trapping sidestream smoke inside the tobacco rod, or finally by a more complete combustion of sidestream smoke. Various techniques to reduce sidestream delivery will be shown, including modification of cigarette design and/or using cigarette papers with specific characteristics. In each case, an attempt will be made to attribute the observed reduction of sidestream "tar" delivery to one or more of the three mechanisms. All measurements of sidestream smoke presented were made using the fish tail collection method proposed by Proctor (1998).