The aim of the research was to identify the motives behind the investment decisions of manufacturing enterprises in Poland in 1996-2003. The analysis was conducted with the use of probit models and an extensive body of panel data applying to individual enterprises to determine the probability of an investment decision. The author discovered that three key factors encouraged investment by manufacturing enterprises in all the surveyed groups (exporters, publicly traded companies, private domestic and foreign enterprises and companies with foreign capital). The first factor is the expected demand for an enterprise’s products, reflecting prospective sales possibilities. Another important factor is the use of production capacity, reflecting the company’s possibilities for expanding its volume of production on the basis of existing resources and assets. Both these factors are complementary with regard to the description of the investment process. Enterprises wanting to expand their sales tend to make investment decisions when their existing fixed assets are insufficient to increase the supply of products. The third key factor that determines investment decisions is prior involvement in a long-term investment process and the continuation of work in progress. In light of the research, the cost of raising funds and the restrictiveness of monetary policy are only loosely related to the course of investment processes in Poland.