Most stars are born as clusters in Giant Molecular Clouds (hereafter GMCs), and therefore the understanding of the evolution of GMCs in a galaxy is one of the key issues to investigate the evolution of the galaxy. The recent state-of-the-art radio telescopes have been enabling us to reveal the distribution of GMCs extensively in the Galaxy as well as in the nearby galaxies, and the physical properties and the evolution of the GMCs leading to cluster formations are actively being investigated. Here we present studies of spatially resolved GMCs in the Galaxy and in the Magellanic Clouds(LMC/SMC), aiming at determining the origins of the observed turbulence and assessing the role of gas interaction in triggering star formation by the observations spanning a range of scales and environmental conditions.