An understanding of the nature and significance of tumour capsules may give added perspective to our understanding of the processes of tumour invasion and metastasis. The commonly held concepts of capsule pathogenesis (the expansive growth and foreign body hypotheses) should probably be discarded as they are not supported by experimental evidence. Indeed, our military terminology of tumour ‘invasion’ and host ‘defence’ may be wholly inappropriate in describing the complex interactions that occur between tumour and host, as tumour growth and invasiveness frequently seem to represent a subtle utilization or perversion of normal physiological mechanisms rather than antagonistic interchanges. The value judgements associated with the terms ‘true’ and ‘false’ capsules also give an entirely wrong perspective of the complexities of tumour biology at the tumour-host interface. There is certainly no evidence to suggest that the relationship between capsule formation and benign behaviour is ‘cause and effect’, but rather both are likely to represent parallel manifestations of common underlying tumour-host interactions. The enhancement of tumour encapsulation has been regarded by some as a future therapeutic goal; the key, however, will not lie in the enhancement of fibrogenesis or tumour immunogenicity, but rather in the manipulation of those tumour-host interactions that lead to invasive growth.