Nanosized molecular sieves or colloidal zeolites are crystalline porous solids with particle sizes in the range of 10-1000 nm; they are synthesized from colloidal precursor solutions under hydrothermal conditions at temperatures lower than 100 °C. The complex mechanism by which nanosized microporous materials are assembling from framework constituent precursor species under heating is investigated by in situ dynamic light scattering, X-ray diffraction using synchrotron radiation, high resolution transmission electron microscopy, and IR/Raman spectroscopies. The development of new crystallization methods that allow the fabrication of zeolites in forms suitable for practical utilization, such as thin films, layers, and monoliths based on the seed method and spin coating approach is discussed. In situ X-ray measurements of zeolite crystal growth simultaneously in solutions and films are performed, in which near surface depth-sensitive grazing incidence diffraction is combined with the in situ growth of thin zeolite films that is ideally suited to shed light on the unresolved mechanisms of self-organized channel orientation for various zeolite systems. In addition, the nanosized Faujasite (FAU) zeolite was employed as host for the stabilization of guest molecules such as 2-(2'-hydroxyphenyl)benzothiazole (HBT); the trans keto tautomer of HBT inside the FAU zeolite is demonstrated and compared with the cis keto tautomer formed in ethanolic solution.