**1. Introduction**

Diverse types of materials such as polymers, glasses, metals, ceramics, zeolites, etc., could be prepared as thin films with high optical quality thus finding applications in photonics, optical sensing, photocatalysis, optoelectronics, linear and non-linear optics, holography, etc. Different production strategies, including "dry" and "wet" deposition methods, are developed and optimized. In order for these thin films and structures to be utilized in different optical devices, unambiguous methods for design and characterization are required. Additionally, in-situ optical monitoring of their properties will be beneficial for proper device operation.

This Special Issue covers the recent progress and new developments in the area of design, deposition, characterization and application of optical thin films and structures.
