This special issue provides a selection of excellent survey articles regarding ongoing research on signal and information processing approaches to security and privacy problems, which complement traditional cryptographic services. The tutorial-style articles survey the challenges associated with achieving security and privacy in both communications networks as well as distributed systems and identify signal processing approaches to protect information. In addition in this issue of SPM, you will notice a "new" column that we call "Reflections." The idea behind this column is not totally original, because SPM published "Leadership Reflections" between March 2003 and November 2006. The authors of the columns were leaders within the signal processing community, such as current or former deans of engineering colleges or managers in industry, who shared their experience, perspectives, and views on future developments and key elements of success.