Pseudomonas aeruginosa is one of the key bacterial pathogens that cause acute, chronic, and lethalinfections in the lungs of patients with cystic fibrosis (CF). P. aeruginosa adheres to the mucosal epithelium of the airways to initiate infections, eventually internalizing and establishing a niche. Ca²⁺ is a potent cellular signal has been shown to exist in abundance in pulmonary fluids of CF patients and trigger the expression of virulence factors in P. aeruginosa. However, its role in the regulation of host-pathogen interactions is not well understood. In this dissertation, we study the role of Ca²⁺ in adherence, invasion, and intracellular replication of P. aeruginosa in lung epithelial cells and its role in the regulation of virulence factors (expression of virulence genes, flagella, and biofilm production) during infection. Two human lung epithelial cell lines, A549 and CuFi-5 (homozygous for the Δ508 mutation in CF) cells infected with PAO1 and FRD1 strains in low and high Ca²⁺ conditions were used for this study. We employ the adhesion assay, immunofluorescence, and scanning electron microscopy (SEM) to study the adhesion of P. aeruginosa to lung epithelial cells. The data suggests a significant increase in adherence in high Ca²⁺ with both cell lines. A similar observation was made with the invasion and escape studies. Ca²⁺ binding protein, EfhP, is reported to regulate invasion, intracellular survival, and escape, whereas it plays an insignificant role in adherence. Transcriptome sequencing (RNA-seq) and quantitative RT-PCR analysis also help to understand the importance of Ca²⁺ in the regulation of adhesin transcription (fliC, pilA and lecA), but this response depends on bacterial strains and the cell line. The Ca²⁺-dependent upregulation of fliC leads to an increased proportion of flagellated bacteria within a population. Ca²⁺ also upregulates other virulence factors of P. aeruginosa that could aid biofilm production, biomineralization, and the production of reactive oxygen species. Here, we provide evidence for P. aeruginosa host cell escape and Ca²⁺-mediated activation of P13K and Akt that results in P aeruginosa invasion and intracellular survival within lung epithelial cells. Our study provides insight into understanding the regulatory potential of Ca²⁺ and Ca²⁺ binding protein, EfhP, in P. aeruginosa infections during CF.