Purpose: The purpose of this research is to examine how Management Control Systems (MCS) impact Diversification Strategy Processes (DSP) in diversified firms. Method: A qualitative research method was used where five different profiled managers participated in the research. The interviews were semi-structured and secondary data were used together with the findings where secondary data was available. Thematic analysis was used throughout the data analysis. Conclusion: The results are inconclusive regarding the impact of the Belief, Interactive, and Diagnostic Controls on the Initiation, Searching, and Execution Stage of DSP. The findings are, however, consistent with the impact of Boundary Controls on the Initiation, Searching, and Execution Stage of DSP. Research Limitations: This research has not differentiated between different types of diversification strategies and their processes. Small, medium, and large firms have not been separated throughout the research. The sample size of the data collection was small, making the results not generalizable.