The discovery of gamma-rays, and thus powerful relativistic jets in narrow-line Seyfert 1 galaxies (NLS1) challenge our current knowledge of active galactic nuclei (AGN). NLS1s differ from other gamma-ray emitting AGN; they have lower mass black holes, higher accretion rates, preferably compact radio morphology, and they reside mostly in late-type galaxies. These differences force us to revise AGN unification and evolution schemes, but NLS1s also offer a new perspective on the jet phenomena. Despite their high importance, NLS1s are a poorly studied class of AGN. A surprisingly large fraction of them are radio-loud and possibly host jets, but some of them seem to be totally radio- silent. This, along with other observational evidence, implies that they do not form a homogeneous class. However, it remains unclear what is triggering the radio loudness in some of them, but, for example, the properties of the host galaxy and the large-scale environment might play a role. I present the results of an extensive study of a large sample of NLS1s. Using various statistical methods, for example, multivariable correlations and principal component analysis, we examined the interplay between their properties, such as emission properties, black hole masses, large-scale environments, and their effect on radio loudness. I also present the first results of the Metsähovi Radio Observatory NLS1 galaxy observing programme.