This chapter focuses on analyzing the performances achieved in the development of capacitance- and impedance-based humidity sensors. Two options for paper-based (PB) sensors, differing in the use of sensitive materials, are considered. The first uses a paper substrate as a sensitive element, and the second uses inorganic materials and polymers applied to a paper substrate as humidity-sensitive materials. Approaches that can be used in the manufacture of sensors are described. It has been shown that functionalization of paper allows expanding a range of relative humidity (RH) levels and improving the sensitivity of humidity sensors. Cellulose-based sensors are also under consideration in this chapter. It is concluded that paper- and cellulose-based, low-cost capacitive and impedance humidity sensors have parameters acceptable for practical use in aggressive humid environments where quick response and long-term operation are not required.