diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bee8a64
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+__pycache__
diff --git a/frontend/exploration.py b/frontend/exploration.py
index 123a22b..43d8c72 100644
--- a/frontend/exploration.py
+++ b/frontend/exploration.py
@@ -13,6 +13,7 @@ uploaded_file = st.file_uploader("Upload your CSV file", type=["csv"])
 
 if uploaded_file is not None:
     st.session_state.data = pd.read_csv(uploaded_file)
+    st.session_state.working_data = st.session_state.data
     st.success("File loaded successfully!")
 
 
diff --git a/frontend/mvstrategy.py b/frontend/mvstrategy.py
new file mode 100644
index 0000000..81db2f8
--- /dev/null
+++ b/frontend/mvstrategy.py
@@ -0,0 +1,70 @@
+from abc import ABC, abstractmethod
+from pandas import DataFrame, Series
+from pandas.api.types import is_numeric_dtype
+from typing import Any, Union
+
+class MVStrategy(ABC):
+    """A way to handle missing values in a dataframe."""
+
+    @abstractmethod
+    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
+        """Apply the current strategy to the given series.
+
+        The series is described by its label and dataframe."""
+        return df
+
+    @staticmethod
+    def list_available(series: Series) -> list['MVStrategy']:
+        """Get all the strategies that can be used."""
+        choices = [DropStrategy(), ModeStrategy()]
+        if is_numeric_dtype(series):
+            choices.extend((MeanStrategy(), MedianStrategy()))
+        return choices
+
+
+class DropStrategy(MVStrategy):
+    #@typing.override
+    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
+        df.dropna(subset=label, inplace=True)
+        return df
+
+    def __str__(self) -> str:
+        return "Drop"
+
+
+class PositionStrategy(MVStrategy):
+    #@typing.override
+    def apply(self, df: DataFrame, label: str, series: Series) -> DataFrame:
+        series.fillna(self.get_value(series), inplace=True)
+        return df
+
+    @abstractmethod
+    def get_value(self, series: Series) -> Any:
+        pass
+
+
+class MeanStrategy(PositionStrategy):
+    #@typing.override
+    def get_value(self, series: Series) -> Union[int, float]:
+        return series.mean()
+
+    def __str__(self) -> str:
+        return "Use mean"
+
+
+class MedianStrategy(PositionStrategy):
+    #@typing.override
+    def get_value(self, series: Series) -> Union[int, float]:
+        return series.median()
+
+    def __str__(self) -> str:
+        return "Use median"
+
+
+class ModeStrategy(PositionStrategy):
+    #@typing.override
+    def get_value(self, series: Series) -> Any:
+        return series.mode()[0]
+
+    def __str__(self) -> str:
+        return "Use mode"
diff --git a/frontend/pages/normalization.py b/frontend/pages/normalization.py
new file mode 100644
index 0000000..4f20c7a
--- /dev/null
+++ b/frontend/pages/normalization.py
@@ -0,0 +1,23 @@
+import streamlit as st
+from mvstrategy import MVStrategy
+
+if "data" in st.session_state:
+    data = st.session_state.data
+    st.session_state.data = data.copy()
+
+    for column, series in data.items():
+        missing_count = series.isna().sum()
+        choices = MVStrategy.list_available(series)
+        option = st.selectbox(
+            f"Missing values of {column} ({missing_count})",
+            choices,
+            index=1,
+            key=f"mv-{column}",
+        )
+        # Always re-get the series to avoid reusing an invalidated series pointer
+        data = option.apply(data, column, data[column])
+
+    st.write(data)
+    st.session_state.working_data = data
+else:
+    st.error("file not loaded")
diff --git a/frontend/pages/visualization.py b/frontend/pages/visualization.py
index 057b0c9..6ca8270 100644
--- a/frontend/pages/visualization.py
+++ b/frontend/pages/visualization.py
@@ -5,8 +5,8 @@ import seaborn as sns
 st.header("Data Visualization")
 
 
-if "data" in st.session_state:
-    data = st.session_state.data
+if "working_data" in st.session_state:
+    data = st.session_state.working_data
 
     st.subheader("Histogram")
     column_to_plot = st.selectbox("Select Column for Histogram", data.columns)