The dynamic interplay between virulence factors of a pathogen and immune system of a host determines whether disease will occur. A deep understanding of the molecular mechanisms that underlie host-pathogen arms race is essential for developing durable resistance. Recent research in my laboratory focuses on plant small RNAs (sRNAs) as a newly emerged battleground in plant-pathogen interactions. Wenbo will discuss our current progress on sRNA-mediated plant immunity and mechanisms employed by the devastating Phytophthora pathogens that suppress this immunity.