By definition, the companion-animal niche demands merely that animals must provide companionship. At first glance, this may seem easy enough, but the forces that contribute to success in this niche are complex. Indeed, success as a companion is rarely measured in terms of biological fitness, and empirical measures of the breeding value of stock remain elusive. The challenges in the niche are manifold and reflect the need for companion animals to show behavioural flexibility, an attribute variously labelled compliance, tolerance, and even forgiveness. The borders of the niche are blurred and there is often negligible communication between buyers and suppliers of companion animals. In addition, demand for a given phenotype is subject to considerable flux. Paradoxically, companion animals may be victims of their own success. We value the social feedback they provide and yet often leave them alone for lengthy periods. There is an inherent tension between the desire to share the company of these animals and the reality that some humans find an animal's need for social contact, and indeed many species-specific behaviours, unacceptable. Also, the animal-sense of owners may be declining, reflecting reduced community exposure to animals in non-companion contexts, such as on farms and as modes of transport. Often, in the case of dogs, the companion-animal niche is occupied by a breed that was developed to work in a specific role that required endless energy and high reactivity. We select for conformation and movement in what were once working animals and yet many owners reject animals for behavioural traits that were subject to scarcely any primary selection. Since neutering of companion animals is, for many excellent reasons, now so common, the genes of outstandingly suitable pets are routinely lost to the gene pool. Companion animals may be living longer and yet, as they age, the dog-human relationship can shift diametrically. Senior dogs often become less appealing to and yet more dependent on, and needful of attention from, their owners. In Australia, urban companion-animal ownership per capita is declining in tandem with falls in living space. Despite this reduced demand, the pet industry uses positive imagery and targeted research to promote pet acquisition, helping to maintain a situation in which supply generally exceeds demand. This results in the annual euthanasia of thousands of excess animals in shelters and pounds. The pet industry also motivates owners to be consumers so it is unsurprising that expenditure on pets in Australia is rising. Sometimes food is promoted as a means of demonstrating affection. In many developed nations, unfortunately, pet owners have the resources to respond to marketing (among other forces) by overfeeding animals, often to the point of obesity. Obesity is considered to be a significant welfare problem for companion dogs. In summary, it seems that these shifts and growing paradoxes are making the companion-animal niche more challenging than ever. Perhaps science will help make the niche more predictable, but this alone will not guarantee the welfare of the animals that occupy it.