The ability of the courts to assess expert evidence is a cause for concern prevalent in western legal systems today. It seems to cut across the traditional divide between Anglo-American and continental European legal systems. The principal form in which that concern is manifest is discussion of expert bias. Bias is of course something that is not unique to experts; it is quite likely that witnesses will be biased, and it is always possible that a judge will be biased. Different legal systems handle these concerns in different ways: some jurisdictions may exclude the testimony of civil parties, criminal defendants or those in certain relationships to them, others may let the question of witness bias go to weight; judicial bias may be dealt with by recusal, or addressed on appeal. The possibility of bias in the testimony of experts is problematic for the courts in a different way from bias in the testimony of witnesses of fact, and it cannot be addressed, as it can for judges, on appeal, and only rarely through recusal.