In this presentation, we will first give a brief introduction to GEO and GEOSS, i.e., the organization and the observing system, respectively. The acronym GGOS covers both the organization and the observing system, and we will introduce the two facets of GGOS. As organization, GGOS provides an umbrella for the many Services of IAG, and as an observing system it is a pivotal contribution to Earth observation. In our consideration of the main aspects of the relation between GGOS and GEO/GEOSS we will in particular focus on the contribution of GGOS to some of the Communities of Practice that have emerged in the frame of GEO. We will conclude with some comments on the mutual benefits between GGOS and GEO/GEOSS.