In this paper we report recent works, realized in our laboratory, dealing with the complex mechanisms ruling the gas-liquid flow in trickle-bed columns. We first emphasize the relationships between the hydrodynamics at the particle scale- where the fluid phases interact with the solid phase- and the hydrodynamics which may be observed at the bed scale. We propose a model based on the concept of random packing accessibilities which relate the liquid flow maldistribution to two main phenomena : the constraint induced by the liquid distributor and the local partial wetting. We present then two experimental techniques enabling to check the soundness of these theorical developments. The first one consists in local liquid flowrates measurements. The comparison between experiments and theory is direct and quite satisfying. A second technique has been recently experimented. It consists in X-ray tomography applied to the determination of the spatial distribution of the gas-liquid-solid phases in a cross section of the column. The first results are very promising, specially to go further in the analysis of the complex interactions between the hydrodynamics and the packing morphology.