Companies around the world spend sometimes many millions for the implementation of ERP-systems (Enterprise Resource Planning systems are used by big organizations and companies for integrated business operation in finance, logistics and human resources) in projects lasting over several years. Nevertheless many of these systems do not deliver the expected benefits. Especially after going live, which is the beginning of the postimplementation phase, in most cases a performance drop can be observed, which lasts for months.

There is a special research area in literature known as „benefit management”, which deals with this problem. Despite comprehensive theoretical concepts benefit management is not common in practice so that the problem of benefits realisation persists even 30 years after the introduction of ERP systems to the market.

The goal of this thesis is to investigate the benefits realisation for ERP-systems after going life (postimplementation phase) in the real world based on the Mixed Methods Approach.

In the qualitative part of the study 44 end users from four industrial companies and ERP consultants were interviewed to find out how benefits materialize, how benefits can be measured and quantified by means of key performance indicators (KPI) and how benefits can be realised over the entire life cycle. These interviews were evaluated using the Qualitative Contents Analysis of Mayring.

In the quantitative part of the study a set of 12 KPIs (inventory value of raw materials, stock turnover rate of raw materials, cycle time of productions orders, cost deviation of production orders, inventory value of finished goods, stock turnover rate of finished goods, lead time of customer orders, delivery reliability, percentage of customer orders delivered in time, duration of monthly financial closing, number of IT tickets and system usage), which were downloaded as monthly measurement values directly from ERP-systems, was analysed for four participating case study companies over a period of 24 months after going live using SPSS software for statistical evaluations.

The result shows that the implementation of an ERP-system is not finished with going live, but requires permanent efforts for benefits realisation to optimize and adjust business processes, provide ongoing end user trainings and further development of an ERP-system in order to exploit the benefit potential of an ERP-system during the whole lifecycle in the best way.

The results of the study show the time dependence of the KPIs and that they can be improved by certain measures. Therefor the author proposes a concept for a benefit controlling to support benefits realisation over the entire life cycle of an ERP-system based on a regular evaluation of a set of processual KPIs.