In the case of Hasegawa v. Kitamura (G.R. No. 149177, November 23, 2007; 563 Phil. 572 [Third Division, Per J. Nachura]), the Supreme Court clarified that the field of private international law generally encompasses three principal areas of inquiry: (a) jurisdiction; (b) choice of law; and (c) recognition and enforcement of judgment.

First, it involves the question of jurisdiction, concerning the determination of which judicial forum possesses the competence to adjudicate a case involving a foreign element. This addresses the application of rules that delineate the circumstances under which a court can legitimately assert authority over foreign individuals or entities. For example, a Philippine court would need to consider Philippine laws on jurisdiction -- primarily governed by Batas Pambansa No. 129 -- to determine if it can properly hear a case brought against a Japanese corporation whose commercial activities in the Philippines are solely conducted through online sales.

Second, choice of law is the meat of private international law. As a process, it focuses on the selection of the particular law, whether municipal law or foreign law, that should govern the substantive rights and obligations of the parties. Choice of law often presents the most intricate aspect of private international law. To illustrate, in the aforementioned contract between the Filipino citizen and the Japanese corporation, Philippine choice-of-law rules for contractual obligations would dictate whether Philippine or Japanese contract law should govern the interpretation and enforcement of their agreement, potentially considering factors such as the place of contract formation, the place of performance, and the expressed or implied intentions of the parties.

Lastly, private international law addresses the process of recognition and enforcement of foreign judgments, which involves determining the extent to which a judicial decree rendered by a court in one sovereign state will be acknowledged and given effect by the courts of another. For instance, if a Japanese corporation obtains a favorable judgment against a Filipino citizen from a Japanese court, the enforceability of that judgment against the Filipino citizen's assets located within the Philippines would be contingent upon Philippine legal principles concerning the recognition and enforcement of foreign judgments, which often consider principles of reciprocity, due process, and compatibility with Philippine public policy. This is directly addressed, for instance, by Section 48 of Rule 39 of the Rules of Court.

In the process of determining the proper law, courts employ various "connecting factors" in relation to "choice-of-law rules." These are more-or-less established legal principles that serve to link the factual circumstances of a case to a specific legal system. Common examples include lex loci contractus (the law of the place where the contract was made), lex loci solutionis (the law of the place of performance), lex loci delicti commissi (the law of the place where the tort was committed), lex situs (the law of the location of property), lex patriae (the law of a person's nationality), and lex domicilii (the law of a person's domicile), which are traditional approaches in choice of law. Contemporary approaches also include the "state with the most significant relationship test," which entails a comprehensive evaluation of which jurisdiction maintains the closest connection to the legal issue in dispute, considering a multitude of relevant factors, and the doctrine of "center of gravity."

The significance of private international law in an increasingly interconnected world cannot be overstated. It provides an essential framework for the orderly resolution of disputes arising from cross-border interactions, thereby fostering a greater degree of certainty and predictability in international commerce, personal relationships, and other legal interactions. Furthermore, by striving to apply the law of the jurisdiction with the most substantial connection to a particular dispute, it aims to achieve outcomes that are perceived as more equitable and just than would result from the invariable application of local law. Finally, the principles of private international law encourage and facilitate cooperation among different legal systems in the recognition and enforcement of judicial decisions, thereby contributing to a more stable and cohesive international legal order. For this, there exist international conventions to ensure recognition and enforcement in one state of the judicial decisions of another.