This paper introduces the concept of Π-regular variation, a generalization of regular variation. A function $U: R^{+} \to R^{+}$ is said to be Π-regularly varying with exponent $\alpha$ if $U(x)x^{-\alpha}$ is nondecreasing and there exists a positive function $L$ such that $$ \frac{U(\lambda x)/\lambda^{\alpha}-U(x)}{x^{\alpha}L(x)}\to\log\lambda\quad(x\to\infty)\mathrm{f o r}\lambda>0. $$ The paper proves that $U$ is II-regularly varying if and only if its Laplace-Stieltjes transform $\hat{U}(t)$ is II-regularly varying. The paper also generalizes Karamata's theorems A and B for nondecreasing functions $U$. It defines $\Pi RV_{\alpha}$ as the class of functions $U$ such that $U(x)/x^{\alpha} \in \Pi$. The paper then proves a theorem that shows that for $\alpha > 0$, $\beta \geq 0$, and $U$ satisfying certain conditions, the following statements are equivalent: $U(x) \in \Pi RV_{\beta}$, $U(x) \in \Pi RV_{\alpha+\beta}$, and $\hat{U}(1/x) \in \Pi RV_{\beta}$. The paper also provides a second order version of Karamata's theorems for nondecreasing functions $U$. The paper concludes with a proof of the main theorem and discusses the implications of the results.This paper introduces the concept of Π-regular variation, a generalization of regular variation. A function $U: R^{+} \to R^{+}$ is said to be Π-regularly varying with exponent $\alpha$ if $U(x)x^{-\alpha}$ is nondecreasing and there exists a positive function $L$ such that $$ \frac{U(\lambda x)/\lambda^{\alpha}-U(x)}{x^{\alpha}L(x)}\to\log\lambda\quad(x\to\infty)\mathrm{f o r}\lambda>0. $$ The paper proves that $U$ is II-regularly varying if and only if its Laplace-Stieltjes transform $\hat{U}(t)$ is II-regularly varying. The paper also generalizes Karamata's theorems A and B for nondecreasing functions $U$. It defines $\Pi RV_{\alpha}$ as the class of functions $U$ such that $U(x)/x^{\alpha} \in \Pi$. The paper then proves a theorem that shows that for $\alpha > 0$, $\beta \geq 0$, and $U$ satisfying certain conditions, the following statements are equivalent: $U(x) \in \Pi RV_{\beta}$, $U(x) \in \Pi RV_{\alpha+\beta}$, and $\hat{U}(1/x) \in \Pi RV_{\beta}$. The paper also provides a second order version of Karamata's theorems for nondecreasing functions $U$. The paper concludes with a proof of the main theorem and discusses the implications of the results.