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diff --git a/date-fns/src/getISOWeekYear/index.ts b/date-fns/src/getISOWeekYear/index.ts
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+import toDate from '../toDate/index'
+import startOfISOWeek from '../startOfISOWeek/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name getISOWeekYear
+ * @category ISO Week-Numbering Year Helpers
+ * @summary Get the ISO week-numbering year of the given date.
+ *
+ * @description
+ * Get the ISO week-numbering year of the given date,
+ * which always starts 3 days before the year's first Thursday.
+ *
+ * ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
+ *
+ * ### v2.0.0 breaking changes:
+ *
+ * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
+ *
+ * - The function was renamed from `getISOYear` to `getISOWeekYear`.
+ *   "ISO week year" is short for [ISO week-numbering year](https://en.wikipedia.org/wiki/ISO_week_date).
+ *   This change makes the name consistent with
+ *   locale-dependent week-numbering year helpers, e.g., `getWeekYear`.
+ *
+ * @param {Date|Number} date - the given date
+ * @returns {Number} the ISO week-numbering year
+ * @throws {TypeError} 1 argument required
+ *
+ * @example
+ * // Which ISO-week numbering year is 2 January 2005?
+ * const result = getISOWeekYear(new Date(2005, 0, 2))
+ * //=> 2004
+ */
+export default function getISOWeekYear(dirtyDate: Date | number): number {
+  requiredArgs(1, arguments)
+
+  const date = toDate(dirtyDate)
+  const year = date.getFullYear()
+
+  const fourthOfJanuaryOfNextYear = new Date(0)
+  fourthOfJanuaryOfNextYear.setFullYear(year + 1, 0, 4)
+  fourthOfJanuaryOfNextYear.setHours(0, 0, 0, 0)
+  const startOfNextYear = startOfISOWeek(fourthOfJanuaryOfNextYear)
+
+  const fourthOfJanuaryOfThisYear = new Date(0)
+  fourthOfJanuaryOfThisYear.setFullYear(year, 0, 4)
+  fourthOfJanuaryOfThisYear.setHours(0, 0, 0, 0)
+  const startOfThisYear = startOfISOWeek(fourthOfJanuaryOfThisYear)
+
+  if (date.getTime() >= startOfNextYear.getTime()) {
+    return year + 1
+  } else if (date.getTime() >= startOfThisYear.getTime()) {
+    return year
+  } else {
+    return year - 1
+  }
+}