Establishing the circuitry underlying attentional and oculomotor control is a long-standing goal of systems neuroscience. The macaque lateral intraparietal area (LIP) has been implicated in both processes, but numerous studies have produced contradictory findings. Anatomically, LIP consists of a dorsal and ventral subdivision, but the functional importance of this division remains unclear. We injected muscimol, a GABA(A) agonist, and manganese, a magnetic resonance imaging lucent paramagnetic ion, into different portions of LIP, examined the effects of the resulting reversible inactivation on saccade planning and attention, and visualized each injection using anatomical magnetic resonance imaging. We found that dorsal LIP (LIPd) is primarily involved in oculomotor planning, whereas ventral LIP (LIPv) contributes to both attentional and oculomotor processes. Additional testing revealed that the two functions were dissociable, even in LIPv. Using our technique, we found a clear structure-function relationship that distinguishes LIPv from LIPd and found dissociable circuits for attention and eye movements in the posterior parietal cortex.