A taxpayer who is carrying on an “adventure or concern in the nature of trade” and has revenue over the Goods and Services Tax (GST) registration threshold is potentially subject to a substantial GST liability. While it is accepted that the reference to an “adventure or concern in the nature of trade” in the GST legislation is aimed at making the proceeds of certain isolated transactions subject to the GST regime, there is very limited Australian guidance regarding which isolated transactions will be affected. This article explores the origins of the term, relevant Australian and United Kingdom authorities, as well as the potential impact of the neutrality principle, which some suggest is a principle of interpretation that is applicable to the GST legislation. In doing so, it clarifies this under-researched area of law by identifying the important principles that determine when a transaction is likely to constitute such an adventure or concern for GST purposes.