The modern day e-society inherently depends on Critical Infrastructures (CI) such as power grid, communication, transportation etc. For such CIs to operate efficiently, Supervisory Control and Data Acquisition (SCADA) systems direct their control and monitoring functionality. However, the technological shift is towards commercial-off-the-shelf SCADA systems that are also increasingly interconnected with each other primarily over dedicated network but slowly tending to even Internet level connectivity. This introduces new communication-level threats and vulnerabilities to SCADA systems. Therefore, the disputed concept "security through obscurity" is no longer applicable, and previously unnoticed or ignored security issues might now be exposed. To handle such security challenges, techniques from conventional networked systems are also being adopted to the SCADA domain. This chapter discusses both adopted and newly developed techniques to secure communication in monolithic as well as highly interconnected systems. © 2012 Springer-Verlag Berlin Heidelberg.