2 laboratory-scale reactor systems suitable for gas phase, and for solution or slurry polymerisations are discussed. The underlying concept behind the design and use of these reactors is that they can be used to understand the impact of conditions specific to different time scales and/or length scales inherent to large reactors that are difficult to recreate at the laboratory scale. For instance the fixed bed gas phase reactor is used to study the influence of different relative gas/solid velocities on the evolution of the molecular weight distribution of the nascent polymer. It is shown that in certain conditions, changing the heat transfer characteristics does not change the observed yield, but will impact the polymer properties. In the case of the solution reactor, the concept is to design and use a reactor to study the activation of unsupported metallocenes. Here it is shown that different metallocenes have very different activation profiles to a point where a stopped flow reactor might not be the ideal tool for their study.