This paper presents a three-dimensional conceptualization of conflict of interest (COI) regulation directed towards assuring the impartial and unbiased decision-making of parliamentarians. We distinguish and separately measure (based on a new dataset) COI Strictness, Sanctions and Transparency and show they indeed constitute empirically separate dimensions of parliamentary ethics regimes adopted in European democracies. To illustrate the usefulness of our indices, we examine the relationship between them and trust in national parliaments across 25 democracies. Unlike our Sanction and Transparency Index, the COI Strictness Index (composed of strictness of rules and enforcement) has a significant and robust negative association with trust, which highlights the importance of disentangling different elements of COI regimes. While future research has to explore the causal relationships between COI regulation and trust, capturing the complexity of COI regimes in an unbiased fashion and thereby making them comparable across European democracies is an essential step towards doing so.