The NSF funded Theory and Practice of Accountable Systems (TPAS) Project investigates computational and social properties of information networks necessary to provide reliable assessments of compliance with rules and policies governing the use of information. In past research, we have demonstrated that achieving basic social policy goals in open information networks will require increased reliance on information accountability through after-the-fact detection of rule violations. This approach stands in contrast to the traditional mechanisms of policy compliance in network environments that rely on security technology to enforce rules by denial of access to resources at risk of abuse. So, access-based systems must be supplemented with accountability-based systems. To ensure that accountable systems can provide a stable, reliable, trustworthy basis on which to ground social policy arrangements in the future, it is necessary: (i) to research practical engineering approaches to designing these systems at scale, (ii) to develop a theory of the operating dynamics of accountable systems in order to establish what types of accountability assessments can be made, when those assertions are reliable, and (iii) to identify what vulnerabilities accountable systems may have to attack, intrusion and manipulation.