The aim of the dissertation is to verify whether innovative small and mediumsized companies are financially constrained in Poland. Companies are classified as financially constrained when they face a wedge between the internal and external costs of funds and are not able to obtain financing freely from external sources to implement all projects (capital as well as R&D) that have been planned due to unavailability of funds. Financial constraints result from the disturbance of capital supply, and their main reason is the asymmetry of information between investors and companies. In this situation generally debt seems to be unsuitable for financing innovative entries and equity financing is better, but due to the limitation of funds on equity market, after exhausting the internal funds, innovative companies follow the pecking order theory, and choose debt, when it is available. To verify the hypothesis that innovative SMEs are constrained compared to large companies, which usually leads to reduction in investment, two research approaches in the studies were employed: direct and indirect measures of financial constraints. Direct measures assume to employ a survey to investigate whether the company has a problem with capital access. The second, indirect measures, depend on the analysis of managers' decisions ex post relating to investment undertaken by companies and assumes that when a company is financially constrained, its capital and R&D investments are sensitive to cash-flow changes. The hypothesis was verified based on the data collected from the survey and financial reports. Financial statements (from Amadeus databases - Moody's Analytics Company) covered approximately 1500 firm-year observations (for 403 companies) in the period from 2011 to 2014. When the financial constraints were measured directly the binary and ordered probit models were used, whereas in case of indirect approach, panel models with fixed effects were employed. The key issue in the research was to measure the innovativeness of companies. Because the research sample covers SMEs which do not register R&D in financial statement, the information on innovative activities was collected by means of a survey. The measures of innovativeness can be generally classified into three groups: input (e.g. R&D expenditure, R&D department), intermediate (e.g. patents) and output measures (e.g. product, process, marketing and organizational innovation). Based on this information and using k-means, cluster and development patterns methods the innovation index was designed. The assumption was adopted that innovation potential is gradable, however, using the same information the companies were also divided into two groups - innovative and non-innovative (control group). The "onedimensional" measures were also used to test which features of innovative activity have the most significant impact on financial constraints. The result from the direct approach is that the higher the innovative potential of the enterprise, the more likely financial difficulties are. The estimated models based on the survey (self-assessment of problems with capital access) and financial data, also confirmed that particularly medium-sized companies are financially constrained. This group is characterized by the highest innovative potential (confirmed also by the value of the innovation index) and, on the other hand, may experience a higher marginal cost of capital than larger entities, which have better access to capital market, and small companies, which can use various preferential forms of financing. The probability of financial constraints rises when a company has an R&D department, bears internal and external R&D expenditures, introduces new, changed service products to the market, and has a patent granted. On the other hand, the problem with capital access is less likely in case of the following activities: introduction of process innovation, changed product, new service or organizational changes. The indirect measures of financial constraints were based on the investment model (accelerator and error-correction model - ECM). The capital expenditure or investment in fixed assets were dependent whereas cash-flow was an independent variable in parallel with the variable that controlled future demand (e.g. sale growth) and other features, such as cash holding, the debt level and previous capital expenditure. There were over a dozen models estimated, and based on the analysis of the results the hypothesis was confirmed. The innovative SMEs are financially constrained compared to non-innovative peers (SMEs and large companies). Based on the results and literature review some implications for pro-innovative policy were defined in the dissertation. Since small and medium-sized innovative enterprises implement projects in response to changes in the internal cash flow, the tools that will increase the pool of internally generated funds, as tax reliefs linked with innovative activity (R&D) and other solutions, such as accelerated amortization, should be considered as effective in alleviating financial constraints problems. However, also preferential loans are recommended as well improvements in the capital market.(original abstract)