The objective of the book is to prepare polyaniline thin films through plasma polymerization technique and their electrical & optical characterization.It is also aimed to investigate their technological applications for detection of hazardous gas analyte such as NO2.To achieve this, we investigated the preparation of aniline thin film via plasma polymerization technique involving such as a brush-shape atmospheric pressure plasma source, low-pressure direct current(DC)plasma polymerization,and low-pressure radio frequency (RF)plasma deposition.Atmospheric pressure plasma brush was used to examine its sterilization and modification efficiencies of low-temperature plasma process without vacuum limitation required in traditional low-pressure plasma systems.The RF plasma deposition was produced on glass substrate for improving their scratch-resistance in optical applications. The conductivity of PANI thin films was also studied by their response characteristics after exposure to nitrogen dioxide.The results obtained has showed that the PANI thin film has tremendous sensitivity towards nitrogen dioxide vapors and shows a maximum response for a voltage of 3.5 volts applied to the sensor.