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diff --git a/src/main/java/org/apache/commons/math3/fitting/leastsquares/LeastSquaresOptimizer.java b/src/main/java/org/apache/commons/math3/fitting/leastsquares/LeastSquaresOptimizer.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.math3.fitting.leastsquares;
+
+/**
+ * An algorithm that can be applied to a non-linear least squares problem.
+ *
+ * @since 3.3
+ */
+public interface LeastSquaresOptimizer {
+
+    /**
+     * Solve the non-linear least squares problem.
+     *
+     *
+     * @param leastSquaresProblem the problem definition, including model function and
+     *                            convergence criteria.
+     * @return The optimum.
+     */
+    Optimum optimize(LeastSquaresProblem leastSquaresProblem);
+
+    /**
+     * The optimum found by the optimizer. This object contains the point, its value, and
+     * some metadata.
+     */
+    //TODO Solution?
+    interface Optimum extends LeastSquaresProblem.Evaluation {
+
+        /**
+         * Get the number of times the model was evaluated in order to produce this
+         * optimum.
+         *
+         * @return the number of model (objective) function evaluations
+         */
+        int getEvaluations();
+
+        /**
+         * Get the number of times the algorithm iterated in order to produce this
+         * optimum. In general least squares it is common to have one {@link
+         * #getEvaluations() evaluation} per iterations.
+         *
+         * @return the number of iterations
+         */
+        int getIterations();
+
+    }
+
+}