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Hippocampal subfield CA3 is thought to stably store memories in assemblies of recurrently connected cells functioning as a collective. However, the collective hippocampal coding properties that are unique to CA3 and how such properties facilitate the stability or precision of the neural code remain unclear. Here, we performed large-scale Ca2+ imaging in hippocampal CA1 and CA3 of freely behaving mice that repeatedly explored the same, initially novel environments over weeks. CA3 place cells have more precise and more stable tuning and show a higher statistical dependence with their peers compared with CA1 place cells, uncovering a cell assembly organization in CA3. Surprisingly, although tuning precision and long-term stability are correlated, cells with stronger peer dependence exhibit higher stability but not higher precision. Overall, our results expose the three-way relationship between tuning precision, long-term stability, and peer dependence, suggesting that a cell assembly organization underlies long-term storage of information in the hippocampus. [Display omitted] • Ca2+ imaging allows studying place cells' precision, stability, and collective coding • Place cells in CA3 exhibit more precise and stable tuning than place cells in CA1 • CA3 displays a collective organization into correlated place cell assemblies • High correlations with cell peers underlie high tuning stability, but not precision Sheintuch et al. study the three-way relationship between precision, stability, and assembly organization of hippocampal place cells. Place cells in CA3 exhibit more precise and stable tuning than in CA1 and display a stronger cell assembly organization. The assembly organization contributes to stability, but not precision, of hippocampal spatial coding. [ABSTRACT FROM AUTHOR]