The comfortable perception that global environmental challenges can be met through marginal lifestyle changes no longer bears scrutiny. The cumulative impact of large numbers of individuals making marginal improvements in their environmental impact will be a marginal collective improvement in environmental impact. Yet we live at a time when we need urgent and ambitious changes. If those in government, business or the third sector persist in advocating ‘simple and painless' behavioural changes as a meaningful response to today's most pressing environmental challenges, this must be because they are persuaded that such changes will encourage the adoption of other, and particularly other more ambitious, behaviours. The effect by which adoption of one pro-environmental behaviour may increase people's inclination to adopt other pro-environmental behaviours, including political engagement, is known as ‘positive spillover'. The particular instance of positive spillover where a behavioural change increases a person's inclination to adopt a second and more ambitious behavioural change is called the ‘foot-in-the-door' effect. Insistence on the use of positive spillover (and particularly foot-in-the-door) strategies legitimises a reliance upon simple and painless behavioural changes, and has undeniable attractions: it can serve to deflect pressure for government to adopt ambitious and potentially unpopular policies and regulations; it allows businesses to claim they are contributing meaningfully to engaging a problem such as climate change through the sale of compact fluorescent light bulbs or washing-lines; and it helps to relieve environmental NGOs of the (potentially upsetting) obligation to draw attention to the full scale and urgency of global environmental problems. These attractions perhaps go some way to explaining the continued reliance placed on positive spillover and foot-in-the-door, even though the empirical evidence for the effectiveness of these strategies is highly contested. While some researchers suggest that pro-environmental conduct has a tendency to spillover from one behaviour to another, others argue that when people engage in pro-environmental behaviour (perhaps a simple and painless step), they often use this fact to justify not doing other (perhaps more environmentally significant) things. Yet other researchers emphasise the uniqueness of every pro-environmental behaviour and downplay the possibility that pro-environmental conduct in one area will have any implications – whether positive or negative – for the likelihood of acting pro-environmentally in other areas. The empirical evidence for spillover – both positive and negative – and the theories offered to explain these results are reviewed. We do not argue that positive spillover and foot-in-the-door effects cannot occur – clearly they do, at least under some circumstances. However, we do not find evidence that positive spillover and foot-in-the-door effects occur with the dependability that would be necessary to responsibly advocate their use as a major plank in engaging environmental problems (such as climate change) that require urgent and ambitious interventions. It seems very dangerous to premise environmental campaigns on an insistence that the adoption of ‘simple and painless' steps will necessarily spillover into ambitious behavioural change proportional to the scale of the challenge. Our concern is that, at present, many campaigns for small and environmentally insignificant behavioural changes are tacitly justified through an unexamined assumption that these will contribute to delivery on more ambitious and environmentally relevant changes. Environmental campaigners should be clear with themselves about whether a campaign is aimed at delivering a specific behavioural change (the actual focus of the campaign) or whether it is aimed at helping to elicit a wider set of behavioural changes (through positive spillover effects). This discipline would oblige campaigners to be clear about two things: first, the inadequacy of responses to environmental problems that rely upon widespread adoption of marginal reductions in individual carbon footprint; and second, the challenges facing them if they are to use such campaigns as vehicles for promoting more ambitious changes. Notwithstanding this overall conclusion, we reflect on the implications of research in spillover for the design of environmental communications and campaigns, with a view to optimising the possibility of positive spillover occurring. This leads to a series of recommendations. A central conclusion is that the reasons underlying the adoption of a particular behaviour have an important bearing on an individual's inclination to adopt further behavioural changes. In particular, an appeal to environmental imperatives is more likely to lead to spillover into other pro-environmental behaviours than an appeal to financial self-interest or social status. This contradicts the insistence, often made by campaign advisers, that environmental communicators should be indifferent to the reasons they use to urge behavioural change. At least to the extent that a campaign aims to encourage spillover into other behaviours, the reasons given as motivation for the initial behaviour are likely to be very important. Moreover, in striving for clarity about the reasons for advocating a particular behavioural change, it is important to focus exclusively on the environmental imperatives. Appealing simultaneously to several incentives (e.g. the financial savings and environmental benefits arising from energy-efficiency measures) is likely to reduce the instance of positive spillover into other pro-environmental behaviours. In the final section of the paper, we examine the possibility that, as a result of engaging in simple and painless behaviours, individuals may be more accepting of proposals for government intervention to enforce these and other pro-environmental behaviours. There is little evidence from empirical studies to draw on here, but we propose that the reasons given to incentivise the initial simple and painless behavioural choices are again likely to be important. In general, we speculate that an individual who has experienced a degree of cost or inconvenience in the course of voluntarily adopting a pro-environmental behaviour for environmental reasons will be more likely to support government interventions to enforce that behavioural change more widely than will an individual who adopts a behavioural change for self-interested reasons. Finally, we reflect briefly on the effect that campaigns for ‘simple and painless' voluntary behaviour changes are likely to have on public attitudes towards ambitious new government interventions, even when these are framed in explicitly environmental ways. Unfortunately, there is currently a lack of evidence to discriminate between the possible effects that ‘simple and painless' campaigns may have on these public attitudes.