This thesis addressed the need for advancing methods that combine time series imagery from medium resolution SAR and optical satellite imagery for improving forest monitoring in the tropics. The main scientific contributions include the introduction of three novel SAR-optical approaches for monitoring deforestation and forest degradation. All three showed improvements over single-sensor systems. For the first time, SAR-optical methods were presented that exploit the full observation density of time series data. We demonstrated their robustness when dealing with persistent cloud cover in the tropics. This enabled the transition from annual to sub-annual change and NRT change detection. Furthermore, an approach for multi-model land cover dependent SAR slope correction was proposed. The last part of this thesis reflects on key aspects and limitations of the introduced SAR-optical approaches and discuss further opportunities and developments.