Along with a general redirection of values in agriculture, the need for action arises for veterinary medicine and other life sciences to establish suitable tools for the objective assessment of housing conditions with regard to their appropriateness concerning animal welfare. First communication between the disciplines involved demands a uniform use of terms. Assessment can be carried out generally either directly by using pathological, physiological and ethological reactions of the animals as criteria or indirectly by the means of technical criteria. Both approaches can indicate poor or good conditions with regard to animal welfare and are generally agreed upon. However using these measures in practise often yields problems referring to the methodology and to the results that are hard to interpret. Criteria referring to the state of the animals have a reduced meaningfulness due to the following aspects: A lot of criteria are lacking sensibility and specificity, which leads to a small diagnostic selectivity. A large number of sources for variance aggravate the use of reference values in order to distinguish between normal or abnormal levels. In many cases there is a lack of firm evidence that the level of changes correlates with the health and welfare of the animals. Due to contradictions caused by the differing properties of the variables being measured the measures do not always co-vary. Results and conclusions of the assessments are closely connected to the specific experimental design and cannot easily be transferred to the housing conditions in practice showing a large variance. Therefore criteria referring to the animals can be used primarily for the assessment of standardized or serial produced housing systems, where a direct comparison between systems is permissible. In order to find out the weak points of the housing conditions concerning animal welfare, on-farm assessment can be carried out more advantageous by using design criteria. Those criteria can be divided into structural and technical elements on the one hand and management born factors like hygiene, climate and feeding on the other. The use of structural and technical elements as criteria ensures a high level or repeatability of the results and practicability in the application. However, a confinement to structural and technical elements went along with a marked reduction in the meaningfulness of the assessment. The use of management born factors is governed by the specific situation. The variation of results depend to a high degree on the time of evaluation. Statements of the real situation within a longer period of time therefore require great efforts. Due to the complex phenomenon there is justified concern that a comprehensive assessment and conclusion referring to the appropriateness of housing conditions concerning animal welfare is not possible. Few criteria cannot be equated with the whole. However, partial statements can be achieved under a scientific point of view using a mixture of different criteria. In order to integrate and weigh the varied results reached by different criteria, a systemic approach and an integrative way of diagnosis is needed. Up to now there is a lack in matured concepts that put the integrative approach of assessment into practice.