Systems science is concerned, among other things, with functional wholes, interactive parts and exchange with the systems environment. What does it mean to observe systems science itself with respect to these aspects? What function does systems science have within the landscape of sciences? What do the various systemic sub-disciplines contribute to a united systems science? In this paper the following will be attempted: - Indicating a set of interrelated system principles. Using this set to clarify the special characteristics and contributions of the sub-disciplines of systems science. - Localizing systems science within the landscape of sciences and indicating relevant connections.