This thesis considers economic agents that borrow under collateral constraints and studies some of the relevant macroeconomic implications. Two chapters are devoted to an analysis of the international transmission of shocks. Recent literature shows that this transmission is due to the fact that, under financial integration, constrained investors purchase domestic and foreign assets. In the first of the two chapters, I extend this mechanism in order to capture the role of cross-border funding. I build a model where investors choose not only their portfolios of home and foreign claims, but also those of home and foreign liabilities. The solution for portfolios presents some innovative advancements and shows that international debt flows (under borrowing constraints) do affect the transmission of shocks. The second of the two chapters, relaxing a commonly made assumption, focuses on the case in which the pledgeable home and foreign assets in investors’ portfolios have different collateral values. A solution method is proposed, where the heterogeneous pledgeability is generated by the riskiness of collateral assets over the short-run. This riskiness affects the transmission of shocks through asset prices and return premiums, especially in case of financial shocks. In the last part of my work, I instead address a different question. Studying the borrowing constraints implied by the regulatory requirements imposed on bank capital, I examine how the governance of banks could be affected by the recently proposed system of countercyclical restrictions (Basel III). Developing a model with inside and outside bank ownership, I find a negative effect. In upturns, the capital requirement increases in accordance with the regulatory policy, and the owners compensate this increase with an increase in their ownership share relative to that of outsiders.