We examine the nature of Collaborative Networked Organizations in Government (CNO-G) and identify three core capabilities characterising such organizations - Partnership, Coordination and Integration. By considering these capabilities as idioms for the CNO-G domain, we define a conceptual model that expresses such capabilities using modeling abstractions provided by ARCON (A Reference Model for Collaborative Networks). Finally, we illustrate the resulting domain-specific modelling framework through the example of a concrete CNO-G aimed at delivering a seamless public service.