diff --git a/TODO.md b/TODO.md
index 0834fb0..e42d239 100644
--- a/TODO.md
+++ b/TODO.md
@@ -45,16 +45,16 @@ After completing a milestone, create a pull request with your changes for review
 
 ## PR4: Data Visualization Module
 
-- [ ] Set up visualization framework
-- [ ] Implement histogram/density plots
-- [ ] Create scatter plot functionality
-- [ ] Add bar chart and pie chart generators
-- [ ] Implement box plots and violin plots
-- [ ] Create heatmap functionality
-- [ ] Add visualization customization options
-- [ ] Implement visualization export capability
-- [ ] Write tests for all visualization functions
-- [ ] Test visualization rendering with different data inputs
+- [x] Set up visualization framework
+- [x] Implement histogram/density plots
+- [x] Create scatter plot functionality
+- [x] Add bar chart and pie chart generators
+- [x] Implement box plots and violin plots
+- [x] Create heatmap functionality
+- [x] Add visualization customization options
+- [x] Implement visualization export capability
+- [x] Write tests for all visualization functions
+- [x] Test visualization rendering with different data inputs
 
 ## PR5: Model Training - Classification
 
diff --git a/tests/test_viz.py b/tests/test_viz.py
new file mode 100644
index 0000000..266b7dd
--- /dev/null
+++ b/tests/test_viz.py
@@ -0,0 +1,53 @@
+import pandas as pd
+from utils import viz
+
+
+def sample_df():
+    return pd.DataFrame({
+        'num1': [1, 2, 3, 4, 5],
+        'num2': [5, 4, 3, 2, 1],
+        'cat': ['a', 'b', 'a', 'b', 'a'],
+    })
+
+
+def test_histogram_and_density():
+    df = sample_df()
+    fig = viz.histogram(df, 'num1', bins=2, title='Hist')
+    assert fig.layout.title.text == 'Hist'
+    fig = viz.histogram(df, 'num1', density=True)
+    assert fig.data[0].histnorm == 'probability density'
+
+
+def test_scatter_plot():
+    df = sample_df()
+    fig = viz.scatter_plot(df, 'num1', 'num2', color='cat', title='Scatter')
+    assert fig.layout.title.text == 'Scatter'
+    assert fig.data[0].marker.color is not None
+
+
+def test_bar_and_pie_charts():
+    df = sample_df()
+    bar = viz.bar_chart(df, 'cat', 'num1')
+    pie = viz.pie_chart(df, names='cat', values='num1')
+    assert bar.data and pie.data
+
+
+def test_box_and_violin():
+    df = sample_df()
+    box = viz.box_plot(df, x='cat', y='num1')
+    violin = viz.violin_plot(df, x='cat', y='num1')
+    assert box.data and violin.data
+
+
+def test_heatmap():
+    df = sample_df()
+    fig = viz.heatmap(df, title='Heat')
+    assert fig.layout.title.text == 'Heat'
+
+
+def test_export_figure(tmp_path):
+    df = sample_df()
+    fig = viz.bar_chart(df, 'cat', 'num1')
+    out = tmp_path / 'chart.html'
+    viz.export_figure(fig, out)
+    assert out.exists() and out.stat().st_size > 0
diff --git a/utils/__init__.py b/utils/__init__.py
index 9ac963c..aa655b5 100644
--- a/utils/__init__.py
+++ b/utils/__init__.py
@@ -3,5 +3,6 @@
 from . import config
 from . import data
 from . import eda
+from . import viz
 
-__all__ = ["config", "data", "eda"]
+__all__ = ["config", "data", "eda", "viz"]
diff --git a/utils/viz.py b/utils/viz.py
new file mode 100644
index 0000000..1087f4c
--- /dev/null
+++ b/utils/viz.py
@@ -0,0 +1,103 @@
+"""Data visualization utilities."""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Optional
+
+import pandas as pd
+import plotly.express as px
+import plotly.graph_objects as go
+
+
+def histogram(
+    df: pd.DataFrame,
+    column: str,
+    *,
+    bins: int = 20,
+    density: bool = False,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a histogram or density plot for a column."""
+    histnorm = "probability density" if density else None
+    fig = px.histogram(df, x=column, nbins=bins, histnorm=histnorm, title=title)
+    return fig
+
+
+def scatter_plot(
+    df: pd.DataFrame,
+    x: str,
+    y: str,
+    *,
+    color: Optional[str] = None,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a scatter plot."""
+    fig = px.scatter(df, x=x, y=y, color=color, title=title)
+    return fig
+
+
+def bar_chart(
+    df: pd.DataFrame,
+    x: str,
+    y: str,
+    *,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a bar chart."""
+    fig = px.bar(df, x=x, y=y, title=title)
+    return fig
+
+
+def pie_chart(
+    df: pd.DataFrame,
+    names: str,
+    values: str,
+    *,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a pie chart."""
+    fig = px.pie(df, names=names, values=values, title=title)
+    return fig
+
+
+def box_plot(
+    df: pd.DataFrame,
+    x: str,
+    y: str,
+    *,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a box plot."""
+    fig = px.box(df, x=x, y=y, title=title)
+    return fig
+
+
+def violin_plot(
+    df: pd.DataFrame,
+    x: str,
+    y: str,
+    *,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a violin plot."""
+    fig = px.violin(df, x=x, y=y, box=True, title=title)
+    return fig
+
+
+def heatmap(
+    df: pd.DataFrame,
+    *,
+    columns: Optional[list[str]] = None,
+    title: Optional[str] = None,
+) -> go.Figure:
+    """Return a correlation heatmap for the given columns."""
+    cols = columns or df.select_dtypes(include="number").columns.tolist()
+    corr = df[cols].corr()
+    fig = px.imshow(corr, text_auto=True, title=title)
+    return fig
+
+
+def export_figure(fig: go.Figure, path: Path) -> None:
+    """Export a figure to an HTML file."""
+    fig.write_html(str(path))