The evolution of wireless handsets from simple mobile phones to smart devices, capable of capturing multimedia information and accessing Internet, has enabled its users to share multimedia contents with other network-capable devices in the vicinity or across the Internet. However, multimedia contents may include private information that a user would share only if it is secure from sniffing and other digital attacks. The same scenario is factual for video transmission from security IP cameras as it may be open to public and many other applications unless secured. Achieving security by fully encrypting multimedia contents (using Virtual Private Networks or otherwise) is not a viable solution, particularly for mobile devices, as they run on limited battery power and employ relatively slower processors compared to their desktop counterparts. These limitations have forced the handsets manufacturers to move the security operations to other parts of the networks thus compromising scalability as well as privacy. This dissertation investigates scalable, power efficient selective encryption techniques for secure real-time streaming of multimedia contents coded using different audio and video codecs. Specifically, selective encryption techniques are proposed for RTP streams, OGG streams, G-729 coded VOIP streams, and VLC coded multimedia streams. The structural properties of codecs and network containers are exploited to identify a subset of bits in the media that are important for the decoding process. Subsequently only these subsets are encrypted to realize security of the entire bit stream. The proposed solutions do not require media decoding, and encrypt on the average less than 5% of the packet load, while still providing robust security equivalent to that of a fully encrypted bit stream. These schemes are ubiquitous to the end users and can be deployed at any node in the network without compromising privacy of the contents. The security properties of the proposed schemes are demonstrated by analyzing the computation complexity for different digital attacks on the partially encrypted streams. The results show that it will take exhaustive combinations/trials to play out the digital media in the absence of encryption key. The performance evaluation is conducted on different platforms such as desktop computers, laptops, netbooks, and handlheld smart devices to consider the effects of computation power and battery capacity. The proposed scheme is compared with full encryption schemes based on different encryption methods, including AES and Chaotic maps.