There is ever more computer power and available data, but sometimes the right data are still missing or difficult to obtain. At the same time, novel infectious disease threats are being identified with alarming regularity while some well-known endemic diseases remain threats. I’ll talk through specific challenging examples including the need for evidence-based (or at least evidence-informed) decisions in the control of bovine TB and the assessment of control measures for vector-borne diseases such as dengue, Zika and malaria.