Access control for a collaborative business environment not only needs to manage resources of individual collaborator but also needs to integrate, dissociate collaborating domains' users & resources, on-demand. As inter-domain transactions are carried out over the Internet, the transactions need security & privacy. Interoperability mechanisms fall short to comprehensively achieve security & privacy in a manner that is scalable, dynamic, autonomy-preserving, and tractable in ephemeral collaborations, thus risking the manageability and security of overall environment in practice. This book delves into all the practical aspects of access control for a distributed environment. Fundamental concepts are explained with the help of practical scenarios. A spectrum of PKIs & their effects on resulting access control frameworks have been extensively studied. The role of cryptography & its relevance is advocated through our analysis & solutions. This book shall help security architects & consultants in arriving at better design decisions. The investigative scenarios & corresponding solutions presented in this book should help security practitioners to engineer their approaches judiciously.