There are hundreds of clinical decision rules and risk scales published in the medical literature, some more widely adopted than others. Ian Stiell, the father of clinical decision rules, shares with us his views and experiences gained from co-creating some of the most influential CDRs and risk scales to date. He explains the criteria for developing a CDR, the steps to developing a valid CDR, how best to apply CDRs and risk scales to clinical practice, and the hot-off the-press new Ottawa COPD Risk Score and Ottawa Heart Failure Risk Score for helping you with disposition decisions. It turns out that in Canada, we discharge about two thirds of the acute decompensated heart failure patients that we see in the ED, while the US almost all patients with decompensated heart failure are admitted to hospital. Dr. Stiell's new risk scores may help physicians in Canada make safer disposition decisions while help physicians in the US avoid unnecessary admissions.