Cyber space is easily the most complex thing humans have ever created. With billions of people and devices all connected together, vulnerability and compromise are inevitable. The complexity continues to grow, and with it comes the emergent insecurity brought by an ever-developing frontier where digital devices and connected people meet. Security challenges present themselves increasingly often and with ever-greater impacts. This is not going to change anytime soon. Although the internet has transformed communication, business, and social life for the better, the construct of 'cyber space' is incredibly fragile and presents endless risk. Connecting every corner of our lives to those of billions across the world, the frontier is slender between the good and the bad, benefit and catastrophe, real and fake, security and insecurity. Cyber security advice can be confusing, contradictory, and sometimes utterly detached from reality. Too easily, people feel guilty for not knowing what to do, or failing to live up to expectations. People, particularly business leaders and policy makers, must daily make security-sensitive decisions, sometimes unknowingly, without being security experts. Securing the Digital Frontier doesn't offer easy answers, but instead explains sixteen dimensions of this dynamic problem and its current partial solutions. The strong technology of encryption has become commonplace, and is a huge benefit if deployed well: but how can you tell? Programming errors give rise to security problems, but why can we not eliminate them? Privacy is tied up with security, but can the two work against each other? Cyber space is international: how can domestic laws protect us? And what happens when those laws come into conflict with technologies like encryption? Why do you need a punctuation symbol and a capital letter in your password, anyway? Through a grasp of the big picture, through technical and human perspectives, we can begin to explore ways to unwind some of the complexity and find ways to contain the risk.