<p>Ambient pH performs a crucial role in plant immunity, abiotic stress response, and plant growth and development. Plant–pathogen interactions influence a dynamic pH environment. Host acidification and alkalinization are under the regulating actions of acidophilic and alkaliphilic pathogens, respectively. Plasma membrane H⁺-ATPases regulate pH homeostasis, and their activity is modulated during pathogen-associated molecular pattern- (PTI) and effector-triggered immunities (ETI). Recent studies have provided insights into the interplay between pathogens and plants when controlling ambient pH. Here, we review pH dynamics in relation to plant immunity and focus on its relationships with PTI, ETI, stomatal immunity, programmed cell death, calcium ion (Ca²⁺), and reactive oxygen species. Comprehension of the complexity of ambient pH regulation may provide new strategies for plant disease control and sustainable agriculture.</p>