The aim of this chapter is to showcase several important contributions towards identification of techniques for spectrum sharing and coexistence. It is envisaged that such novel techniques may be of value in various regulatory considerations. They might assist in shaping technical conditions that will govern the access to radio spectrum by CR technologies. Section 3.1 reviews the recommended principles of Geolocation Databases’ operation in European regulatory environment, as well as the envisaged structural composition of technical solutions for their implementation. Section 3.2 is composed of several contributions that offer different angles of looking at CR spectrum sensing algorithms and implementation techniques. It also considers the possibilities of dynamic re-configurability through beam forming capabilities. This is followed by discussion in Sect. 3.3 of possibilities for spectrum aggregation from non-contiguous frequency bands, as made possible by the DSA capabilities of CR. This opens up possibilities for significantly increasing the available operational bandwidth—and hence the data throughput—of the radio transceivers. It also allows pursuing energy efficiency objectives. Section 3.4 looks at the possibilities of developing unsynchronised CR networks using Filter Bank Multi-Carrier, an alternative type of modulation that offers a superior performance and reduced out-of-band emissions compared with other traditional types of modulation. The detection of malicious users is addressed in Sect. 3.5, by employing a statistical approach. This approach allows reliable detection of users even when the system does not have a priori information about primary channel activity and characteristics of users. The following Sect. 3.6 looks at the spectral efficiency of CR systems and the related possibilities of using Iterative Water-filling method, which may be highly beneficial for broadband wireless channels under static or slowly varying conditions. The final Sect. 3.7 contains two contributions that present different aspects associated with the issue of assessing the amount of white spaces, or in other words—spectrum resource available for DSA access. It first looks at the principles of Radio Environment Mapping, which is then complemented by an example of evaluating amount of TV band white spaces in Italy.