We develop a model of ESG investing where firms privately differ in their intrinsic ESG commitment: some value the non-pecuniary return from green investment, while others opportunistically greenwash. A pro-ESG lender can include a monitoring covenant that imperfectly detects greenwashing, while firms can alternatively seek financing in a retail financial market. Monitoring disciplines opportunistic borrowers but requires large repayment concessions that also generate informational rents for ESG-oriented firms. Consequently, monitoring adoption is non-monotonic in monitoring capability and may cease when monitoring becomes sufficiently effective. Stronger competition among retail lenders has an ambiguous effect on ESG-monitoring adoption, depending on the pro-ESG lender's best non-monitoring alternative and the value of green investment.