Taking typical ubiquitous computing settings as a starting point, this chapter motivates the need for security. The reader will learn what makes security challenging and what the risks predominant in ubiquitous computing are. The major part of this chapter is dedicated to the description of sample solutions in order to illustrate the wealth of protection mechanisms. A background in IT security is not required as this chapter is self-contained. A brief introduction to the subject is given as well as an overview of cryptographic tools.