Natural selection should favour individuals who are able to adjust their life history strategy and resource allocation in response to changing environmental and social conditions. I examined the flexibility of reproductive resource allocation by female mice in response to manipulation of their nutritional, immunological and social environment. I considered the consequences of their investment decisions for the next generation. In five separate experiments I found that: 1. Food restricted females skewed their offspring sex ratio in favour of sons. 2. Ambient disease cues caused females to produce more resistant and less aggressive sons. 3. Direct parasitic infection prior to pregnancy caused females to produce more resistant sons with an altered hormonal response to socialisation. 4. Dominant females were less likely to become pregnant, suckled litters less post-partum, and produced more aggressive offspring. 5. Despite a mate-choice preference for subordinates, females which were mated with dominant males had bigger litters. These responses by females to variation in their local environment are likely to have fitness consequences for their offspring, and as such would be acted upon by selection. Further work should seek to gain insight into the mechanisms underlying these responses, and determine the adaptive or non-adaptive nature of the flexibility observed.