Poly(methacrylic acid) (PMAA) undergoes a conformational transition between pH 4 and 6 from a hypercoiled structure to a water-swollen state. There has been much speculation as to the exact nature and driving force of the transition. In this paper, we present a comprehensive investigation of the conformational switch of PMAA using techniques which report on various length scales: fluorescence energy transfer experiments provide unique information on the nanometer length scale while dynamic light scattering (DLS) offers an insight into longer range interactions involved in the transition. Fluorescence energy transfer measurements demonstrate that PMAA undergoes subtle molecular rearrangements between pH 2 and 5 as short-range hydrophobic interactions between methyl groups are broken down by increasing concentrations of mutually repulsive carboxylate anions. Although such rearrangements have been proposed to account for the pH behavior of PMAA, we reveal them experimentally using techniques sensitive to nanoscale events. Fluorescence lifetime measurements indicate a rather complex structure within the collapsed chain, and time-resolved anisotropy measurements also demonstrate the importance of intramolecular interactions at low pH. A critical point, at pH 5.7, is reached in terms of the carboxylate anion concentration where a macroscopic transition occurs (as monitored by DLS): the concentration of carboxylate anions is such that repulsive interactions dominate, and a switch occurs from a compact, globular form to an expanded state when neutralization of the PMAA is complete. We conclude that small-scale rearrangements in structure occur between pH 2 and 5, rather than a large-scale expansion, which is then followed by a macroscopic change in dimension at the neutralization point. Our results comprehensively describe the conformational behavior of PMAA and reconcile, to some extent, previous conflicting experimental data in the literature.