diff --git a/MathPad/MPSumFunction.h b/MathPad/MPSumFunction.h
new file mode 100644
index 0000000..4676883
--- /dev/null
+++ b/MathPad/MPSumFunction.h
@@ -0,0 +1,19 @@
+//
+//  MPSumFunction.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 22.04.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPFunction.h"
+
+@class MPSumFunction, MPExpression;
+
+@interface MPSumFunction : MPFunction
+
+@property (nonatomic, strong) MPExpression *startExpression;
+@property (nonatomic, strong) MPExpression *targetExpression;
+@property (nonatomic, strong) MPExpression *sumExpression;
+
+@end
diff --git a/MathPad/MPSumFunction.m b/MathPad/MPSumFunction.m
new file mode 100644
index 0000000..6608bde
--- /dev/null
+++ b/MathPad/MPSumFunction.m
@@ -0,0 +1,120 @@
+//
+//  MPSumFunction.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 22.04.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPSumFunction.h"
+#import "MPExpression.h"
+
+@implementation MPSumFunction
+
+#pragma mark Creation Methods
+
+- (instancetype)init
+{
+    self = [super init];
+    if (self) {
+        _startExpression = [[MPExpression alloc] init];
+        _startExpression.parent = self;
+        _targetExpression = [[MPExpression alloc] init];
+        _targetExpression.parent = self;
+        _sumExpression = [[MPExpression alloc] init];
+        _sumExpression.parent = self;
+    }
+    return self;
+}
+
+#pragma mark Working With the Expression Tree
+
+- (NSUInteger)numberOfChildren
+{
+    return 3;
+}
+
+- (MPExpression *)childAtIndex:(NSUInteger)index
+{
+    switch (index) {
+        case 0:
+            return self.startExpression;
+        case 1:
+            return self.targetExpression;
+        case 2:
+            return self.sumExpression;
+        default:
+            return nil;
+    }
+}
+
+- (NSArray *)children
+{
+    return @[self.startExpression, self.targetExpression, self.sumExpression];
+}
+
+- (void)setChild:(MPExpression *)child
+         atIndex:(NSUInteger)index
+{
+    switch (index) {
+            // TODO: Copy child?
+        case 0:
+            self.startExpression.parent = nil;
+            self.startExpression = child;
+            break;
+        case 1:
+            self.targetExpression.parent = nil;
+            self.targetExpression = child;
+            break;
+        case 2:
+            self.sumExpression.parent = nil;
+            self.sumExpression = child;
+            break;
+        default:
+            return;
+    }
+    child.parent = self;
+}
+
+#pragma mark Evaluating Functions
+
+- (double)doubleValue
+{
+#warning Implementation
+    return 0;
+}
+
+#pragma mark Working With Functions
+
+- (BOOL)isEqualToFunction:(MPFunction *)aFunction
+{
+    if (![aFunction isKindOfClass:[MPSumFunction class]]) {
+        return NO;
+    }
+    MPSumFunction *sumFunction = (MPSumFunction *)aFunction;
+    if (![self.startExpression isEqualToExpression:sumFunction.startExpression]) {
+        return NO;
+    }
+    if (![self.targetExpression isEqualToExpression:sumFunction.targetExpression]) {
+        return NO;
+    }
+    return [self.sumExpression isEqualToExpression:sumFunction.sumExpression];
+}
+
+- (NSString *)description
+{
+    return [NSString stringWithFormat:@"Sum(From: %@; To: %@; Using: %@)", self.startExpression, self.targetExpression, self.sumExpression];
+}
+
+#pragma mark - NSCopying
+
+- (id)copyWithZone:(NSZone *)zone
+{
+    MPSumFunction *copy = [[MPSumFunction allocWithZone:zone] init];
+    copy.startExpression = [self.startExpression copy];
+    copy.targetExpression = [self.targetExpression copy];
+    copy.sumExpression = [self.sumExpression copy];
+    return copy;
+}
+
+@end
diff --git a/MathPad/MPSumFunctionLayout.h b/MathPad/MPSumFunctionLayout.h
new file mode 100644
index 0000000..9750f51
--- /dev/null
+++ b/MathPad/MPSumFunctionLayout.h
@@ -0,0 +1,17 @@
+//
+//  MPSumFunctionLayout.h
+//  MathPad
+//
+//  Created by Kim Wittenburg on 23.04.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPFunctionLayout.h"
+
+@class MPSumFunctionLayout, MPSumFunction;
+
+@interface MPSumFunctionLayout : MPFunctionLayout
+
+- (MPSumFunction *)sumFunction;
+
+@end
diff --git a/MathPad/MPSumFunctionLayout.m b/MathPad/MPSumFunctionLayout.m
new file mode 100644
index 0000000..d001fe5
--- /dev/null
+++ b/MathPad/MPSumFunctionLayout.m
@@ -0,0 +1,35 @@
+//
+//  MPSumFunctionLayout.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 23.04.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPSumFunctionLayout.h"
+#import "MPSumFunction.h"
+
+@implementation MPSumFunctionLayout
+
+- (MPSumFunction *)sumFunction
+{
+    return (MPSumFunction *)self.function;
+}
+
+- (NSSize)calculateSize
+{
+    NSAttributedString *text = [[NSAttributedString alloc] initWithString:@"∑" attributes:@{NSFontAttributeName: [NSFont fontWithName:@"HelveticaNeue" size:50.0]}];
+    [self.textStorage setAttributedString:text];
+    NSRange glyphRange = [self.layoutManager glyphRangeForTextContainer:self.textContainer];
+    return [self.layoutManager boundingRectForGlyphRange:glyphRange inTextContainer:self.textContainer].size;
+}
+
+- (void)drawFunctionAtPoint:(NSPoint)point
+{
+    NSAttributedString *text = [[NSAttributedString alloc] initWithString:@"∑" attributes:@{NSFontAttributeName: [NSFont fontWithName:@"HelveticaNeue" size:50.0]}];
+    [self.textStorage setAttributedString:text];
+    NSRange glyphRange = [self.layoutManager glyphRangeForTextContainer:self.textContainer];
+    [self.layoutManager drawGlyphsForGlyphRange:glyphRange atPoint:point];
+}
+
+@end