My PhD Thesis: In this work we present our contributions to business processes modeling. Namely, we have undertaken a thorough analysis of the OMG standard BPMN, along with other related technologies like WS-BPEL and XPDL. Such analysis has pointed out several weaknesses that motivate our contributions. We propose a new conceptual model of BPMN called BPeX as a clear and principled way to represent and reason about business processes. We provide a three-phase design methodology to model business processes focusing on BPMN and we introduce the notion of business process normal form. We introduce also the concept of business process views and apply them to business processes access control. Finally, we provide an extension to BPMN with privacy policies. Relevant parts of BPMN conceptual model will be included as part of the forthcoming BPMN 2.0 standard.