This thesis investigates trust in companies. Some authors have proposed trust as the explanatory variable for organisational performance. The thesis starts with an overview of how the notion of trust, as an essentially personal phenomenon in Medieval Christianity at the beginning of the millennium, became secularised in early sociology in the first half and economised in the second half of our century. After a literature review, this thesis goes on to show that authors from different social disciplines describe trust in the language and using instruments of social psychology. More specifically, they use the language and instruments of the construct known as `attitude'. The thesis defines trust as attitude: as a psychological tendency that is expressed by evaluating a particular entity with some degree of favour. In the empirical part of the thesis hypotheses on the communicative antecedents of trust toward a company in a population and the consequence of trust for organisational performance are tested on time series data for three companies: British Airways, Shell and The Post Office. Hypotheses establishing functional relationships between media exposure, media favourability, awareness and trust on one side, and between trust and organisational performance on the other side are rejected. In the final chapter results are discussed and four major conclusions are suggested. First, that trust in and around organisations can not account for organisational functional performance, but for organisational contextual performance, which refers to what people do to environments affecting organisational task performance. Second, communication has amplifying effects on trust, but is irrelevant as far as the direction of the trust term is concerned; units of communication have different weights, and thematic analysis is needed to capture it. Thirdly, trust is a multidimensional concept that is composed of the subject's functional components (utilitarian, value-expressive, ego-defensive and knowledge functions) and the trust-object's functional components (ability, capability and willingness). Fourthly, when measuring trust, the principles of aggregation and compatibility developed in the attitude research field need to be respected.